Ok so i just replaced my sending unit for my 56 f100 because the old one was not working and the gauge would always stay on "E". After replacing it the gauge now functions and after only putting in about 3 gallons of gas the gauge reads"full". it is the original gauges and the original type of sending unit. Heres the trivky part, the battery died and had to jump start it with another vehicle and while it was being jumped the gas gauge moved and showed that i had less than a qtr tank and once the jumper cables were removed the gauge went back to reading full. What could the problem be?

My guess would be a loss of continuity somewhere in the ground circuit.  Try a temporary jumper wire from the battery negative terminal to the base of the sending unit.  If the gauge reads correctly, then start backtracing the grounds from the battery to the frame, to the body, to the gas tank, to the sending unit.

John - "The Hoosier Hurricane"

I would agree, has to be a ground someplace, completely different story, but once was repla ing a gage in a old deuce and a half in the army and kept zeroing out. Somehow or another it was grounding to the dash. There was a loose internal wire causing the case to groundHad it out and worked fine and put it back in the dash and nothing. Try taking it out in isolation and see if it works and go from there.

Mike Rizzo

1963 F100 "Rudy"

Daniel Island, SC

If your ground is good you might want to pop the cap off the top of the sending unit and there is a serated adjusting wheel in there that can be adjusted. If the tank was empty and you put three gals in then the gauge should read about empty when you rotate the wheel one way or the other. This wheel was used to calibrate the unit when manufactored and each was set differently. Make note where the wheel is set prior to moving so you can always go back to the origanal factory setting. It's rare they ever need resetting however sitting around 50+yrs things shift. I have a 56 F100 that I had to adjust last week due to a bad reading.

Sam

Another thing to check is the resistance of your sender unit. If your sender unit has been replaced by one of the aftermarket sending units most do not work on a 56. 1956 was the only year that Ford used full 12 volts to the guages so has a very unique sender.



The original sender units usually read ~14-18 ohms full and ~88-95 ohms empty.

The aftermarket senders read ~750 ohms empty and ~75 ohms full so is a big difference. Some of the suppliers even use the B6A part number. These high resistance senders are for cars that have modern guages installed with a voltage reducer or older 6 volt cars or cars that have been converted to 12 volts.



The only after market sender I have found that works is the one Carpenter sells with part number B6A-9275.

marv