Many gas gauge problems relate to the gas tank ground. Before you check anything else make sure the tank itself or at least the sender itself has a ground to the frame. It may be necessary in some cases to add a wire from one of the sender mounting screws to the frame.

55-57's use a 0 to 30 ohm setup that is not the most accurate arrangement and has not been used since the 50's. If you are having problems with accuracy you can correct this to some degree by adjusting the sender arm. This is a trial and error process that you can do after you are sure that both the gauge and the sender are basically functional. For example if the gauge is reading lower than the amount of gas that you know is in the tank, you would raise the gauge reading by bending the float arm down.

To Check Gas Gauge:

1.     Take wire off of tank sender, leave it in the air not touching anything. Turn key on, gauge should go to past full.

2.     Touch sender wire to frame (full ground), turn key on, gauge should read empty. If wiring and tank ground is good then sender is not working.

3.     If you suspect the wiring this check should be repeated by removing wires at gauge.