SECTION 12

CHASSIS ELECTRICAL

CONTENTS OF THIS SECTION

Four separate wiring harnesses comprise the chassis wiring system in all passenger cars. These are: (1) the Dash Harness which is located on the passenger side of the dash panel and is connected to the electrical controls and instrument lighting; (2) the Front Extension Harness which is located in the engine compartment and consists of front lighting, horn and generator control leads; (3) the Grille Extension Harness, which is located on the grille and consists of horn, parking and turn signal leads; and (4) the starting motor to ignition switch harness, which carries cranking motor, ignition primary, temperature and oil pressure leads from the engine compartment to the ignition switch and instrument cluster.

The Dash Harness is connected to the body harness through a multiple pin connector under the instrument panel. The Dash and Front Extension Harnesses are joined through a multiple connector on the left side of the dash, while the Front Extension and Grille Harnesses are connected by a bulkhead connector in the left filler panel between the radiator and fender.

With bulkhead connectors, it is no longer necessary to run wiring through sheet metal. The connectors are the "one-way" type which can be joined in only one position. Individual "multiplug" connectors are used to attach component parts of the system at the main lighting switch, ignition switch, dimmer switch, horn relay and neutral safety switch.

A junction block, which is provided as optional equipment, serves as a central connection for lamps and electrical accessories on the car and includes separate fuses for protection of tail and stop lamps, dome lamp, instrument panel lamps and accessories such as radio, heater and spot lamps. When the junction block is not used, the fuses of the various circuits are installed in the respective line. The headlamp and parking lamp circuits are protected by a single circuit breaker in the instrument panel main lighting switch.

The wiring diagram (fig. 1) shows all electrical units and circuits as well as positions of electrical units which are shown diagramatically. The plastic insulation of each wire is distinctively colored to assist in tracing circuits and making connections.

Additional wiring diagrams on body wiring, convertible top lift and electric window lift circuits are contained in Section I. Circuits peculiar to the overdrive transmission are illustrated in Section 7.

Description and Operation
Sealed Beam Unit Replacement
Headlamp Beam Adjustment
Lighting Switch Replacement
Stoplight Switch Replacement
Dimmer Switch Replacement
Parking Lamp Service
Tail and Stoplight Service

Description and Operation

The lighting and wiring units include the lighting switch, stop fight switch, dimmer switch, glove compartment switch, headlamps and parking lamps, tail and stop lights, license lamp, instrument and indicator lights, wiring harness and all other wiring except that covered under other circuits.

The lighting switch (fig. 2) incorporates a 13 ampere thermal circuit breaker to protect the headlamps and parking lamp wiring, while all other lights on the vehicle are directed through fuses in the respective lines. A current flow of more than 13 amperes will cause the points of this circuit breaker to open and close as they warm and cool. Thus the current to the affected circuit is rapidly interrupted and restored until the short is located and corrected. Protection against destruction of the wiring is thereby provided and possible rapid discharge of the battery averted. Figure 3 shows a circuit diagram for the lighting switch.

When the switch control knob is pulled out to the first position, an internal circuit is established to the switch terminals for the parking lamps, instrument lights and tail lights. When the knob is pulled out to the last position, a circuit is established to the switch terminals for the headlamps, instrument lights and tail lights. The current for, the instrument lights passes through a rheostat which is protected by a 3 amp. fuse and is regulated by the light switch knob. By turning the switch knob clockwise, the instrument lights can be dimmed or turned off completely. The dome lamp may be turned on while retaining use of the instrument panel lights by rotating the lighting switch knob to the extreme counterclockwise position (through the detent or "click").

The mechanically operated stop light switch, located behind the instrument panel and above' the steering column, is attached to the underside of the brace supporting the brake pedal (fig. 21). When the switch is "off" in the pedal released position, the switch plunger is held onto the switch by the pedal arm. When the pedal arm is moved forward to apply the brakes, a spring within the switch causes the switch plunger to follow the pedal, closing the circuit within the switch and lighting the stop lights.

The dimmer switch is located on the toe pare to the left of the clutch pedal. When the headlights are on, this switch is used to change the lights from high to low beam or from low beam to high beam. Each time the switch button is depressed and released the lights are switched from one beam to another.

When the upper beams are in use a red indicator light will be visible through a small opening in the speedometer dial.

Sealed Beam units are the new T-3 Safety Aim Headlamp. This headlamp features better visibility through a brighter beam pattern in both beams. Full advantage of the driving beam is accomplished by the addition of an opaque metal shield built over the front of the lower beam filament which prevents stray light from escaping upward and reflecting back into the driver's eyes.

The T-3 lamp can be identified by the T-3 Trademark and by the three molded aiming lugs protruding from the face of the lamp and located in triangular fashion around the outer edge. The tops of these lugs are precision ground to give a base for the Safety-Aimer to seat upon fig. 9. .

Due to the entirely different method of adjusting T-3 headlamps, the T-3 Safety-Aimer has been developed to be used exclusively on sealed beam units with aiming lugs. In "Safety-Aimer and Headlamp Adjustment" following this description, is a more concise description of the Safety-Aimer and its use.

The Type A Safety-Aimer incorporates an adjustable dial feature which permits a downward adjustment in excess of 2" such as required by the States for truck loading allowances. This dial reads in "inches of down aim" required for 2" for passenger cars to a maximum of 18" for commercial vehicles. A Type A conversion package is available through the Kent Moore Organization under Tool 6412 for adding the adjustable dial to aimer without this feature. All service operations below are performed with the Type A Unit installed on the Aimer.

The sealed beam headlamp (fig. 4) features the T-3 headlamp unit and a redesigned retaining and mounting ring. The retaining ring is held to the lamp body by a spring, eliminating the screw attachment previously used. This feature simplifies sealed beam replacement as well as eliminates confusion that existed between retaining ring screws and adjusting screws (fig. 5). Parking lamps are mounted at both ends of the center bar of the grille. A double filament 4-32 candlepower bulb is used in each parking lamp. All models use combination stop and tail lamps with double filament bulbs having 4 candlepower for the tail light and 32 candlepower for the stop light. The stop light filament is also used as a turn indicator light. The stop light is controlled by the stop light switch and the tail light by the lighting switch. The circuit is so arranged that if the tail and dome lamp fuse interrupts the circuit, the panel lights will also be extinguished, thus warning that the car is without tail light protection.

The rear license plate is mounted on the rear deck lid and is illuminated by a 4 candlepower lamp in the center of the bumper face bar except for station wagon models which have a light in each bumper guard.

The instruments are indirectly illuminated by four small bulbs installed through the back of the cluster. Each individual light socket is fitted with a snap-in feature so that it can be retained to or easily removed from its opening in the cluster. These lights are turned on by the regular light switch and can be dimmed by the light switch rheostat. Generator, oil pressure, direction signal and hi-beam telltale lamps are installed to the cluster in the same manner. See Specifications for bulb information-nation on instrument and indicator lamps.

Sealed Beam Unit Replacement

1. Remove four headlamp door retaining screws and remove door with gasket.
2. Unhook the spring from the retaining ring (fig. 6) and, holding sealed beam unit, retaining ring and mounting ring as an assembly, remove mounting ring from adjusting screws. DO NOT disturb the adjusting screws.
3. Pull assembly forward, disconnect connector plug from sealed beam unit (fig. 7) and remove assembly.
4. While holding mounting ring, lift retaining ring as shown in Figure 8 to release the retaining ring from the retaining ring tab opposite spring attachment of assembly. Remove retaining ring and sealed beam unit from mounting ring. While lifting retaining ring, caution should be exercised to avoid damage to molded lugs on face of T-3 headlamp unit.
5. Place new sealed beam unit in mounting ring and position unit so that "TOP" inscription on front of glass is to the right of retaining ring tab. Index molded lugs on back of sealed beam unit to indentations in mounting ring.
6. Index hole in retaining ring over tab on mounting ring (fig. 8).
7. Connect plug to sealed beam unit ( fig. 7) and engage mounting ring adjusting screw tabs with vertical and horizontal adjusting screws.
8. Engage spring of lamp body in spring slot in retaining ring.
9. Install headlamp door with gasket and install retaining screws.

The T-3 Safety-Aimer (fig. 10) consists of a circular base the size of a sealed beam unit, with three attaching spring loaded hooks protruding through the base which connect onto the retaining ring of the headlamp unit. Attached to the front of the base and extending perpendicular to the base is a "T" type arm; the top of the T arm being a crossarm which is parallel to the ground when mounted on the headlamp bulb. The crossarms are the attaching points for the leveling string between each individual aimer. Mounted on the arm between the base and the crossarm is an adjustable bubble level which may be adjusted to compensate for variation in floor levelness. With the Safety-Aimer, aiming can be accomplished in daylight-the lights do not have to be turned on.

While aiming headlamps, car should be at curb weight, that is with spare tire and filled to capacity with gas, oil and water but no passengers. Tires should be uniformly inflated to recommended pressure.

Before adjusting aim of headlamp bounce car up and down several times and allow to settle. The floor should be reasonably level with enough room to walk around the car. If the area is level the T-3 Aimer can be used as it comes from the factory. Before the Aimer is packaged, the bubbles are set for use on level aiming space. Pads on the base of the Aimer provide a means of checking any given area for levelness.

How to Select a Level Aiming Area

1. Select area you believe to be level.
2. Remove headlamp doors and install Aimer on each headlamp (fig. 15) making sure aiming lugs engage smooth inner ring of the Aimer. To install Aimer, first properly latch the bottom hook, then the top two remaining hooks.
3. Set aiming dial on numeral 2 (fig. 11) and back vertical lamp adjuster out on each lamp until bubble is outside of black line of vial then center bubble in between black lines of vial by turning clockwise (fig. 13).
4. After both bubbles are centered, turn the car around end for end, making sure the tires rest in the spots made on the floor before the car was moved.
5. If the bubbles are still within the two black marks on the vials, the floor is level enough to use the Aimer as it comes from the factory. NOTE: A quick level check can be made by using the T-3 Safety-Aimer as a level. Use with a true eight to ten foot two by four as an extension. Make sure pads on base of Aimer are used. Place the board where you expect the wheels to be and take readings as outlined above.
6. If either bubble moves outside the black lines of the vial there is too much slant to the floor. Try driving the car in at different angles onto the aiming area. If bubbles can not be centered follow procedure under "How to Compensate for Unlevel Floor". NOTE: When level portion of floor is obtained, mark tire spots on floor so spots can be used next time without calibrating Aimer.

If your floor is not level within the limits specified, the T-3 Aimer can be calibrated to compensate for the error in your floor.

Now to Compensate for Unlevel Floors

1. Drive car onto area you know to be level, such as a wheel alignment ramp.
2. Remove headlamp doors and install Aimer on each headlamp (fig. 15) making sure aiming lugs engage smooth inner ring of the Aimer. To install Aimer, first properly latch the bottom hook, then the two remaining hooks. Adjust crossarm of Aimer so it is parallel to floor.
3. Set Aiming Dial on the numeral 2 ( fig. 11).
4. Level bubble by backing out vertical adjuster screw (fig. 13) until bubble is out of black lines of vial. Then turn screw clockwise to center bubble. Repeat operation on other lamp.
5. Remove the T-3 Aimers by unlatching upper two hooks first and lower hook last. Leave headlamp doors off and return car to aiming area which will be used in your place. CAUTION: Do not adjust vertical adjuster screw until Aimer is calibrated.
6. Reinstall Aimers on headlamps (see Step 2 for installation of Aimers). After car has been positioned in aiming area, rock car sideways several times to equalize springs. The bubbles will not be centered.
7. Center the bubble on each Aimer by turning as shown in Figure 12. Aimer is now calibrated for the unlevel area. Mark the tire spots on floor so area can be used again without calibrating aimer.

How to Recheck the Bubbles on T-3 Aimer

Regardless of method used in obtaining satisfactory among surface, the T-3 Aimer is now calibrated for your floor surface. Find some spot on wall or vertical surface that will center the bubbles without adjusting any screws on Aimer. This may require two spots on wall, one for the left hand Aimer and one for the right hand Aimer (fig. 14). Mark the spots for future use so that the Aimer bubbles can be rechecked in case your Aimer is dropped or damaged. This precaution may save you going through all steps previously mentioned.

Headlamp Adjustment-T-3 Headlamp

1. Drive vehicle onto selected aiming area.
2. Remove headlamp doors.
3. Mount T-3 Safety-Aimer on each headlamp so the points of headlamp engage smooth inner ring of Aimer. Be sure to mount left hand Aimer (with string) first. NOTE: On previous vehicles T-3 headlamps must be installed in order to use T-3 Aimer. For 1955 model see "Use of T-3 Headlamp on 1955 Model Cars" in this section of this manual.
4. Fasten Aimer to retaining ring with spring loaded hooks. Lower hook should be fastened first, then the two remaining hooks. The arrow on each knob indicates the direction of the hook. After fastening the three hooks of each Aimer to each lamp the cross bars should be approximately parallel with the ground.
5. With both Aimers in place, fasten spring loaded string across slots from left to right crossbar. Slots can be aligned with string by rotating Aimers around lamp mounting rings as required. The string must be taut to make lamp adjustments.
6. Rock car gently sideways to equalize springs.
7. Rotate Aiming dial so that numeral "2" is at top of dial and in line with pointer (fig. 16).
8. Horizontal Adjustment-All reference letters refer to Figure 17.
   • Rotate aimers around lamp ring so that knotch in aimer arm is bisected by string. Arm should be horizontal.
   • Adjust left headlamp by turning horizontal adjusting screw in or out to make string just touch at arm.
   • Repeat operation on right Aimer by moving horizontal adjusting screw in or out until string touches cross arm.
   • Recheck contact points of arm. If necessary make minor adjustments to have string barely touch.
9. Vertical Adjustment-All reference letters refer to Figure 18.
   • Center bubble by turning vertical adjustment screw. NOTE: To insure proper location, back screw out until bubble is at end of vial. Then turn screw clockwise to center bubble.
   • Repeat operation for other headlamp.
   • Recheck contact points of arms. If both bubbles are still centered, remove Aimers and install headlamp doors.

Use of T-3 Headlamp on 1955 Model Cars

When the T-3 Sealed Beam Headlamps are installed on 1955 model cars, it will be necessary to determine what style retaining ring is used before the T-3 Safety-Aimer can be installed and used for adjusting the headlamps. If the headlamp retaining ring has the aiming lugs attached, it will be necessary to install spring clip, Part No. 5847712, to the ring in the position indicated in Figure 19 to give the unit stability enough to hold the aimer. These spring clips will not be needed when the T-3 lamp is installed on previous models and should only be used on 1955 models with retaining rings constructed as noted above. The clips will be packaged in quantity of 10 per envelope and be distributed under Part No. 5947710.

Lighting Switch Replacement

1. Pull handle out to headlamp position.
2. Reach under the instrument panel and depress the switch shaft retainer (fig. 20) and remove knob and shaft assembly.
3. Remove the retaining ferrule. Also remove the escutcheon and bezel, then remove switch assembly.
4. Disconnect the multi-plug connector from the lighting switch. A screwdriver may be inserted in the side of the switch to pry the plug from the switch.
5. Connect the multi-plug connector to a new light switch.
6. Place switch in position and install the bezel, escutcheon and the ferrule.
7. Push the switch knob and shaft assembly into position so that it snaps into engagement. Check operation of lights.

Stoplight Switch Replacement

Refer to Figure 21.

1. From under the instrument panel adjacent to the brake pedal, disconnect the two switch wires from the connectors.
2. Remove the lock nut from plunger end of switch and remove switch.
3. Locate new switch in same approximate position on brace as switch previously removed.
4. Adjust switch position for proper operation of switch. Electrical contact should be made when brake pedal is depressed 5/8" from fully released position.
5. After proper adjustment, install lock nut, then install the two switch wires to the connector and check operation of switch.

Dimmer Switch Replacement

1. Lift interior floor mat and remove the three screws retaining mounting plate to toeboard.
2. Remove multiplug connector from Dimmer switch, then remove two screws holding switch to mounting plate.
3. Install new switch securely to mounting plate with two screws, then connect multiplug connector to switch.
4. Install mounting plate and switch to toeboard with three screws.
5. Check operation of switch.

Parking Lamp Service

1. To remove bulb, remove the two lens retaining screws then remove lens and bulb.
2. To remove housing:
   • Disconnect bulb housing and wire from grille bar by opening hood and reaching behind grille assembly.
   • Remove two retaining nuts, then remove lamp assembly by pulling forward out of opening.
3. To assemble, reverse procedure above, then test operation of lamp.

Tail and Stop Light Service

1. To remove bulb:
   • Remove three screws retaining lens, then remove lens (fig. 22).
   • Remove and replace bulb.
2. To remove lamp body assembly:
   • Remove nuts retaining rear fender crown molding, then remove crown molding.
   • Remove four nuts retaining lamp housing to fender disconnect harness plug and remove lamp body.
   • To assemble, reverse the above procedure

Instruments and Gauges

Description and Operation
Service Operations

Description and Operation

Generator Telltale Light
Oil Pressure Indicator
Fuel Gauge
Temperature Indicator
Speedometer

The generator telltale light, oil pressure indicator, fuel gauge, temperature indicator and speedometer come under the classification of instruments and gauges.

Generator Telltale Light

The generator telltale light, located in the instrument cluster, is connected in a circuit with the battery and generator through the ignition switch (see fig. 1-Section 6y). When the generator begins to charge, the voltage build up from the generator in the circuit opposes the battery voltage to the indicator light. As the differential between the generator and battery voltage in the circuit continues to decrease, the light will go out. It is emphasized that the telltale light functions primarily as an indicator of generator output, not necessarily of current flow to or from the battery as in the case of the ammeter.

Oil Pressure Indicator

The oil pressure indicator light is located at the right side of the instrument cluster. The light is connected in a circuit with the ignition switch and a pressure operated switch which is located in the main oil gallery on the left side of the engine on the 6-cylinder and adjacent to the distributor on the V-8. The switch is calibrated to close when oil pressure drops to 4-7 psi.

Fuel Gauge

The fuel gauge consists of a dash or indicating unit and a tank unit plus the necessary wiring (fig. 23). The circuit is connected to the ignition terminal of the ignition switch; therefore, it registers only when the ignition switch is on. The dash unit operates on an electromagnetic principle in which magnetic action is opposed by a counterweight on the indicator hand. When the current is OFF the counterweight returns the hand to the "empty" position. When the switch is ON, current flows from the ignition switch to the fuel gauge dash unit, through the choke or limiting coil to the common connection between the two coils. From this point current can travel through the operating coil of the dash unit to ground and also over the wire to the tank unit and through this unit to ground. When the tank is empty the float is near the bottom of the tank and the contact finger will cut out the resistance of the tank unit. Most of the current will then pass to the tank unit and directly to ground while very little current will pass through the dash unit operating coil, therefore causing the gauge to show empty. As more fuel is placed in the tank the float is raised causing the contact finger of the tank unit to move across the resistance unit inserting more coils of resistance in the tank circuit (fig. 23). This additional resistance forces more current through the dash unit operating coil which moves the indicating hand over toward the "full" side of scale.

Temperature Indicator

The electric temperature indicator system consists of an engine thermal plug electrically connected with a registering gauge mounted in the instrument panel. As shown in the wiring diagram in this section on page 2, the gauge and engine unit are energized by the ignition switch circuit, hence the gauge does not register until the switch is turned on.

The engine unit is mounted in the intake manifold near the water outlet connector on V-8 engines and in the cylinder head water jacket (left rear) on six cylinder engines. Engine heat at this point, acts on the element in the thermal plug causing variation in resistance in the electrical circuit. Gauge registers C (cold) and H (hot). Normal operating range is indicated by a band in between C and H on the gauge.

Speedometer

The speedometer and odometer is centrally located in the instrument cluster. The transmission end of the speedometer shaft is slipped into the transmission case with the driven gear coming to rest on the underside at the drive gear. The assembly is retained at the transmission by a key which is bolted to the transmission. The speedometer shaft is attached to the speedometer with a coupling nut.

Instrument Cluster
Generator Telltale Light
Oil Pressure Indicator
Fuel Gauge
Temperature Indicator
Speedometer Service

Instrument Cluster

All component parts of instruments and gauges which are installed to the instrument panel are contained within the cluster. The cluster may be removed from the opening above the steering column, after which any desired instrument or gauge may be detached from the cluster. AU indicator or cluster illuminating lamp bulb sockets are clip retained and may be quickly snapped in or out of position. Fuel, temperature and speedometer gauges are installed to the cluster with screws. Figure 24 shows all connections to the back of the cluster.

Removal

1. Remove two screws on lower steering post cover and remove lower cover.
2. From behind dash, remove nuts from two studs, one on either side of the steering post. On Powerglide or Turboglide equipped models, disconnect indicator rod from lever.
3. Remove the two screws from under hp of instrument panel cluster hood.
4. Pull entire cluster carefully toward rear of car and out of panel opening. Disconnect speedometer and electrical connectors.

Installation

1. With speedometer and electrical connections made, place the cluster assembly in the instrument panel opening.
2. Install the two short screws under the hp of the hood and the nuts on the two studs at either side of the steering post behind the dash. On Powerglide and Turboglide models, install indicator rod to lever.
3. Replace the steering post lower cover.

Ignition on, engine not running and telltale light off-

1. Indicator bulb burned out, replace bulb.
2. Open circuit or loose connection in the telltale light circuit.

Telltale light stays on after engine is started-

1. If light stays on at idle only, check for low idle speed.
2. Check generator output.

If the light does not come on when ignition switch is turned on, or if light stays on after engine is started, either the oil pressure is low or the wiring or a unit in this circuit is defective.

Telltale light on, engine running-

1. Oil pressure low. First check oil level, then if pressure is still low, remove pressure switch and check oil pressure with a reliable pressure gauge.
2. Electric circuit grounded between telltale light and pressure switch.
3. Oil pressure switch not functioning properly. Replace switch.
4. Oil pressure switch calibration wrong. Increase engine speed slightly and check to see if light goes out.

Ignition on, engine not running and telltale light off-

1. Telltale light burned out, replace bulb.
2. Open circuit between light and ignition switch or between light and pressure switch.
3. Pressure switch stuck. Replace switch.
4. Pressure switch not grounded. Check threads of switch for foreign material.

The most common cause of fuel gauge trouble is high resistance in the circuit. Make sure all connections are tight and free from dirt, paint or corrosion.

Since the fuel gauge consists of two remotely located units and the connecting wires, it is sometimes difficult to determine which unit is at fault. A Tool 204 (fig. 25) is available for testing the unit. If a unit is proved to be faulty it should be replaced.

If Tool 204 is not available a tester may readily be made by obtaining a tank unit from parts stock. Attach a spring terminal clip to a 5-foot piece of insulated colored wire and connect the other end of this wire to the binding part of the tank unit. Next, attach two spring terminal clips to a similar piece of black insulated wire and the tester is ready for use.

Testing

• A-1. With the ignition switch "OFF", remove the connector from the left hand terminal (facing the back of the instrument) of the fuel gauge.
• 2. Attach the colored wire of the tester to this terminal and the black wire to a good ground.
• 3. Turn ignition switch to "ON", move tester arm up and down; dash unit should register FULL and EMPTY if it is OK. If so, turn ignition switch OFF and replace the connector.
• 4. If the dash unit does not register at all on above test, make sure that it is getting current from the ignition switch by connecting a 12 volt lamp from ignition terminal on back dash unit to ground.
• B- If dash unit is OK, next check the wiring between dash and tank units as follows:
• 1. Disconnect tank unit wire at the tank unit.
• 2. Attach the colored wire of the tester to the end of the wire removed from the tank unit and clip the black wire to ground.
• 3. If on this test dash unit reads EMPTY at all times or the reading is noticeably lower than during the check at the dash unit, look for shorts or leaks in the wiring between dash and tank. Leaks are most likely to occur at terminal junctions. If dash unit reads above FULL at all times or if it reads higher than EMPTY and FULL than readings obtained when checking at the dash, look for poor connection or break in wiring. Be sure all contacts are clean.
• C-1. If dash unit and wiring check OK, remove tank unit (see Section 8) from tank. Clean away all dirt that has collected around tank unit terminal as road dirt, particularly calcium chloride, causes an electrical leak that will cause an error in reading.
• 2. After cleaning thoroughly, connect tank unit to the wire leading to dash, grounding the tank unit with a short piece of wire from the outer edge to any part of the car. Turn ignition switch ON and move the float arm up and down. If this unit is OK, the dash unit will give corresponding EMPTY and FULL readings.
• 3. If tank unit is OK, reinstall in the tank-if not, replace with a new tank unit but first repeat above test before installing in the tank. NOTE: Always check tank units for freedom of movement of the float arm by raising it to various positions and observing that it will fall to EMPTY position in every instance.

The temperature indicator requires very little attention other than making sure all connections are tight and free of dirt. Since the temperature gauge consists of two remotely located units and the connecting wires, it is sometimes difficult in determining which unit is at fault. The procedure below will aid in your diagnosis.

Testing

1. Disconnect wire at engine unit.
2. Connect a test light consisting of a 12 volt 2 candlepower bulb and a pair of test leads in circuit by clipping one lead to battery terminal on starter and other lead to body of engine unit. If bulb lights, unit is properly grounded. If bulb does not light, check for presence of sealing compound around threads of unit. Remove compound and repeat test. Make sure unit is properly grounded before proceeding with next test.
3. Remove test lead from body of unit and connect lead to terminal of unit. If bulb lights, engine unit is internally short circuited and should be replaced. ;
4. Remove test light and reinstall wire on unit.
5. If engine thermal gauge unit tests satisfactorily under above conditions, check following items according to nature of difficulty:
   • If the gauge does not register when ignition is turned on: This may be caused by a break in the circuit between the gauge and the ignition switch or a short between this lead and ground.
   • If gauge shows high temperature under all conditions: Wire leading from gauge to engine unit is shorted to ground.
   • If gauge registers a low temperature under all conditions: Wire between gauge and engine unit is broken.

Do not attempt to repair either the engine unit or the gauge. When installing new engine unit, do not use thread compound on unit threads, as this will increase electrical resistance of unit and cause faulty reading on gauge.

The speedometer head requires comparatively little service, and as special equipment is required to render this service, most automobile dealers send the speedometer to an authorized AC speedometer service station.

Cable Replacement or Lubrication

1. Disconnect the speedometer cable from the speedometer head and fitting at the transmission. Remove the old cable by pulling it out from speedometer end of conduit. NOTE: If old cable is broken it may be necessary to remove lower piece from transmission end of conduit.
2. Lubricate the lower 3/4 of cable with AC speedometer cable lubricant and push the cable into the conduit. Connect lower end to fitting on transmission and upper end to speedometer head. Road test vehicle for speedometer operation.

Head Replacement

1. Detach and pull instrument cluster assembly from instrument panel opening.
2. Disconnect speedometer cable from head.
3. Remove two instrument lamps and high beam indicator lamp from back of speedometer.
4. Remove the four speedometer assembly to cluster retaining screws and remove speedometer and plate assembly.
5. Remove 2 screws, rubber pad, 2 rubber grommets and 2 grommet retainers connecting speedometer head plate to speedometer head and remove speedometer head.
6. Place rubber pad inside head plate over cable spindle, then install speedometer head in head plate. Push two rubber grommets and retainers through from the outside. Install 2 screws and tighten.
7. Position speedometer and plate assembly on cluster, install four attaching screws and tighten.
8. Connect speedometer cable to head, install lamp bulbs to back of speedometer and assemble cluster to instrument panel opening.

Description and Operation
Service Operations

Description and Operation

The two horns, which are located on the fender skirt baffles on all 1957 passenger car models are designed to give a blended tone when operated together. Each of these horns uses a solenoid actuated diaphragm to actuate a resonating air column in the horn projector.

The horn relay is a magnetically operated switch, remotely controlled by the horn push button switch. This relay completes the circuit directly to the horn through the relay contacts.

When the horn button completes the circuit, a small amount of current flows from the battery through the relay windings. The armature is attracted to the magnetic field, causing the contact points to close. Current from the battery then flows directly across the contact points in the relay to the horn. The relay is used to provide a higher voltage to the horn by avoiding a voltage drop in the long circuit to the horn button.

Quick Checks for Horn Trouble
Horn Replacement and Bench Check
Horn Relay Adjustments

Quick Checks for Horn Trouble

When analyzing faulty horn operation, any of the following three basic conditions may be found:

1. Horn will not operate.
2. Horn operates, but has poor tone.
3. Horn operates intermittently.

Horn Will Not Operate

If the battery checks GOOD, then this condition may be caused by:

1. Defective relay, horn button, or wiring.
2. Defects within the horn (See Bench Checks).

To locate the trouble, connect a jumper lead to the "H" and "B" terminals of the relay (see Figure 29 for terminal location). If the horn blows the trouble is in the relay, horn button, or wiring.

To determine whether the relay, horn button, or wiring is at fault, ground the "S" terminal of the relay (see Figure 29 for terminal location).If the horn blows, the horn button or wiring is at fault. If the horn does not blow and the wiring between the battery and relay is not defective connect a voltmeter between horn terminal and the horn mounting nut. Again connect the jumper lead to the ."H" and "B" terminals of the relay and note the voltmeter reading.

If no voltmeter reading is obtained, the wiring between the relay and horn is open or the horn is not grounded. If the voltmeter reading is less than 7.0 volts, the trouble is due to high resistance connections in the wiring or a faulty horn. If the reading is above 7.0 volts, the trouble is due to a faulty horn which should be removed for a bench check (see Bench Check).

Horn Operates But Has Poor Tone

This condition may result from:

1. Low available voltage at the horn.
2. Defects within the horn (see Bench Check).

Although the horn should blow at any voltage above 7.0 volts, a weak or poor tone may occur at operating voltages below 11 volts. If the horn has a weak or poor tone at an operating voltage of 11 volts or higher, replace the horn.

Horn Operates Intermittently

This condition may result from:

1. Loose or intermittent connections in the horn relay or horn circuit.
2. Defective horn switch.
3. Defective horn relay.
4. Defects within the horn. (See Bench Check.)

Horn Replacement

1. Raise hood and disconnect wire from horn.
2. Remove screw retaining horn and bracket assembly.
3. Install new horn and bracket assembly.
4. Replace wires to horn connections and test, for operation.

Bench Check-Current Adjustment

To check the current adjustment, measure the current draw of the horn while the horn is operating. The low note horn (identified by an odd number in the last digit of the model number) and the high note horn (identified by an even number in the last digit of the model number) should have a current draw of 8.0-10.0 amperes at 11.5 volts.

To make current adjustment, turn adjusting screw as shown in Figure 26. To decrease the current turn the adjusting screw clockwise, and to increase the current turn the adjusting screw counterclockwise.

Horn Relay Adjustments

Three checks and adjustments are required on the horn relay; air gap, point opening and closing voltage. The air gap and contact point opening checks and adjustments should be made with the battery disconnected.

Air Gap-The air gap should not normally require adjustment unless the relay has been misadjusted. Check the air gap with the points barely touching and adjust if necessary by bending the lower point support (fig. 27). Air gap should be .014f".

Point Opening-Check the contact point opening and adjust by bending the upper armature stop (fig. 28). Point opening should be .027".

Closing Voltage-To check the relay closing voltage, connect a variable resistance or potentiometer of sufficient value (not less than 10 ohms) in series with the "B" terminal, connect a voltmeter to the "S" and "B" terminals, and ground the "S" terminal as shown in Figure 29. Slowly decrease the amount of resistance in order to check the relay closing voltage. Closing voltage should be 5.0-9.5 volts. Adjust the closing voltage by bending the armature spring post (fig. 30). Bend down to increase the closing voltage and bend up to decrease the closing voltage.

Description and Operation
Service Operations

Description and Operation

A six wire circuit, which includes a direction signal switch and flasher unit, is used on the 1957 Chevrolet Direction Signal. This circuit utilizes a filament in the parking light for indication at the front and the stop light filament at the rear. Telltale indicators are also provided in the instrument cluster. Current is directed through the flasher unit to the switch, from where it is directed to the desired indicator lamps. A canceling feature is provided in the mechanism to return the switch to the "off" position after completion of a turn. Overload protection is provided within the flasher unit.

Figure 1 shows the direction signal circuit diagram while Figure 31 shows a simplified schematic of the installation together with the operation of the signal switch. Figure 32 shows an exploded view of the direction signal housing and switch assembly.

Service Operation

Adjustments
Trouble Diagnosis

Adjustments

The direction signal switch requires no adjustments due to its simplicity of design. However, if any malfunction of this mechanism should occur, the steering wheel may be removed and the mechanism checked for defective parts. Any defective parts should be replaced.

Trouble Diagnosis

Presented below are a few of the more common direction signal troubles and their probable causes:

1. If indicator light in cluster burns steady or flashes at a very high rate when lever is placed in a turn position-
   • Check for burned out bulb in park or stop lamp.
   • Check for faulty flasher if park and stop lamp bulbs are both on.
2. If indicator light in cluster does not bum when lever is placed in a turn position-
   • Check for burned out indicator light.
   • Check for a faulty flasher.
3. If switch fails to cancel after completion of turn, worn or broken parts within the mechanism in the housing is indicated. The steering wheel should be removed and the mechanism checked for defective parts.
   

Symptom and Probable Cause
Probable Remedy

HEADLAMP AND CIRCUIT


Headlights Dim (engine idling or shut off)

Partly discharged battery.
Charge battery.

Defective cells in battery.
Replace battery.

High resistance in light circuit.
Check headlight circuit including ground connection. Make necessary repairs.

Faulty bulbs.
Replace bulbs or sealed beam units.


Headlights Dim (engine running above idle)

High resistance in lighting circuit.
Check lighting circuit including ground connection. Make necessary repairs.

Faulty bulbs or reflectors.
Test voltage control and generator.

Faulty voltage control unit
Make necessary repairs.


Lights Flicker

Loose connections or damaged wires in lighting circuit.
Tighten connections and check for damaged wiring.

Light wiring insulation damaged producing momentary short.
Check light wiring and replace or tape damaged wires.


Lights Burn Out Frequently

High voltage regulator setting.
Adjust voltage regulator.

Loose connections in lighting circuit.
Check circuit for loose connections.


Lights Will Not Light

Discharged battery.
Recharge battery and correct cause.

Loose connections in lighting circuit.
Tighten connections.

Burned out bulbs.
Replace bulbs or sealed beam unit

Open or corroded contacts in lighting switch.
Replace lighting switch.

Open or corroded contacts in dimmer switch.
Replace dimmer switch.


Thermal Circuit Breaker Causing Current Interruption

Short in headlamp wiring.
Check wiring of circuits in use for short circuits and make necessary repairs.

Short within some light or instrument in use.
Check lights or instruments for short. Headlamps and parking lamps are on separate. circuit breaker from remainder of lighting units.


GASOLINE GAUGE

Gauge Shows Empty at All Times

Tank unit shorted.
Replace unit.

Wire from dash unit to tank unit shorted.
Replace wire or repair short.

Float stuck in empty position.
Replace tank unit.

Dash unit improperly grounded on instrument panel.
Properly ground dash unit.


Gauge Shows Full at All Times

Tank unit burned out.
Replace tank unit.

Wire between units disconnected or broken.
Connect or replace wire.

High resistance in wire between units.
Clean connections and terminals.

Float stuck in full position.
Replace tank unit.


Gauge Does Not Register Accurately (within normal limits)

Bent hand on dash unit.
Replace unit or straighten hand.

High resistance in circuit.
Check and correct circuit.

Partial short in circuit.
Correct cause of short.

Loose electrical connections.
Tighten connections at dash unit and tank unit.


SPOTLIGHT AND CIRCUIT

Will Not Light

Switch faulty.
Replace switch.

Wires broken, disconnected or loose.
Make necessary repairs.

Bulb burned out.
Replace bulb.

Loose connection or poorly grounded lamp body.
Tighten loose connections or properly ground lamp body.

Burned out fuse.
Check for shorts and replace fuse.


HORN AND CIRCUIT

Will Not Blow

Loose connections or broken wire.
Tighten loose connections or replace broken wire.

Horn button not making contact.
Adjust horn button contact.

Faulty horn.
Replace horn.

Defective horn relay.
Replace horn relay.


Horn Tone Poor

Faulty horn.
Replace horn.


Horn Operates Intermittently

Loose connections or intermittent connections in horn relay or horn circuit.
Check connections and repair as required.

Horn switch out of adjustment.
Adjust horn button contact.

Defective horn relay.
Replace horn relay.

Defects within the horn.
Replace horn.


GENERATOR TELLTALE LIGHT

Ignition on, Engine Not Running, Telltale Off

Indicator bulb burned out.
Replace bulb.

Open circuit or loose connection in telltale circuit.
Locate open circuit or loose connection and correct.


Telltale Light Stays On After Engine is Started

If on at idle only, improper idle speed.
Adjust idle speed.

Low generator output.
Check generator output.


OIL PRESSURE INDICATOR

Telltale Light On, Engine Running

Circuit grounded between telltale light and pressure switch.
Locate and correct grounded condition.

Oil pressure switch not functioning properly.
Replace switch.

Oil pressure switch calibration wrong.
Replace switch.

Oil pressure low.
Correct as necessary.


Ignition On, Engine Not Running, Telltale Off

Telltale light burned out.
Replace bulb.

Open circuit between light and ignition switch or light and pressure switch.
Find and correct open circuit.

Pressure switch stuck.
Replace switch.

Pressure switch not grounded.
Check threads of switch for foreign material.

Bulb Specifications                 Candlepower       Number
           Name
Headlamp Unit-Upper......................50 W       Sealed Beam
             -Lower......................40 W       Sealed Beam
Parking Lamp and Direction Signal .....  4-32           1034
Tail and Stop Lamp ....................  4-32           1034
Direction Signal Telltale Lamp ........  2                57
License Plate Lamp ....................  4                67
High Beam Indicator Lamp ..............  1                53
Instrument Cluster Lamp ...............  2                57
Clock Lamp ............................  4                67
Glove Compartment Lamp ................  2                57
Dome Lamp .............................  15             1004
Rear Quarter Lamp-Sport ...............  6                90
Coupe Courtesy Lamp-Convertible .......  6                89
Generator Indicator Lamp ..............  2                57
Oil Pressure Indicator Lamp ...........  2                57
Radio Dial Lamp .......................  2                57
Heater Control Panel Lamp .............  2                57
 
Horn Relay
Air Gap ..............................  .014"
Point Opening ........................  .027"
Closing Voltage ....................... 5.0-9.5 volts

Horns 
Current Draw 
 Low ("L") Horn ........ 8.0-10.0 amperes @ 11.5 volts
 High ("H") Horn ....... 8.0-10.0 amperes @ 11.5 volts

Circuit Protection 
    Name                               < B>Protection
Headlamp-Parking Lamp .................. 13 amp.      circuit breaker 
Panel Lamps-Accessory Lamps ............  3 amp.      fuse 
Tail Lights-Dome Lamp-Glove
Box-Clock-Stop Lamps ...................  9 amp.      fuse
Heater (Without Air Conditioning) ...... 10 amp.      fuse 
Air Conditioning (Includes Heater) ..... 20 amp.      fuse 
Radio ............................... 7 1/2 amp.      fuse 
Backing Lamp ..........................   9 amp.      fuse 
Brake Indicator .......................   9 amp.      fuse 
Underhood Lamp, Courtesy Lamp,
Spot Lamp .............................   9 amp.      fuse 
Power Antenna .........................  14 amp.      fuse