Fuel Gauge

I have a 87 m35A2.
When I turn the power switch on,
The gauge reads what the true fuel level is.
When I start the truck the gauge goes to "F" full.
Any ideas? Gauge? Sending unit?
Thanks for any help.

Hi Bill,
Check the grounds is where I would start.
Tank sender to frame.
Tom

The fuel gauge is a simple set up. I would start by checking and improving the ground. The gauge grounds via the gauge bracket which in turn grounds via the four panel screws. The power feed into the gauge should be firmly attached and not have any damaged insulation where it rubs against the dash or other pieces.
I would then check the plug for the sending unit, also making sure it has good contact (a bit of dielectric grease helps) and is not kinked or broken and has a good ground to the frame.
If it still acts up after that, you can take the sending unit out and move the float arm while soldier B watches the gauge. It should be a linear movement. If it isn't, chances are it is the sending unit that has a bad spot.

You can test the gauge separately.

There is a lso a systematic step by step writeup in the TM TM9-2320-361-20 telling you how to do it: http://www.jatonkam35s.com/DeuceTechnicalManuals/TM9-2320-361-20.pdf
Page 2-124 (part 2, troubleshooting, section VI electrical, failure code 31)



Here is some more reading: https://www.steelsoldiers.com/showthread.php?74734-Fuel-Gauge-Not-Working ; https://www.steelsoldiers.com/showthread.php?10178-Fuel-sending-unit-or-gauge