i have a 78 f250 camper special with a 429 and dual tanks. also is 4x4 if that makes a diff. now, my gauge reads just barely above E and i mean just barely. when i switch the selector on the dash by the heater it doesnt really move at all with it. i have my insturment panel pulled out but have no idea what im looking at. can anyone help me out? i kinda need the gauge to work as i just bought this pick-up and have no idea how fast it uses gas. thanks in advance

 

If it does not work with either tank, I would look at the guage to see if it is getting power, if not check fuses and if fuses are good, I believe your truck has a voltage regulator behind your dash that drops the guage voltage from 12 to about 5 volts.....they sometimes burn out.

 

Okay so where is the voltage regulator and what does it look like. And how do I check to see if I have power at the fuel gauge itself.

 

Beofre you tear into the instrument cluster
More than likely it is a ground issue at the fuel tank sending unit to tank problem

or

an full of fuel float issue

To test the ICVR with the ign key in run ,go to the temp sending unit and look for 5 volt pulsing on the wire to the SU.

If that pulses then the ICVR is fine






Move to wiring of the fuel system,

 

Does the Temperature gauge work? If it does, then it's not the ICVR.

Do all tests with the ignition switch in run. When connecting disconnecting wires, make sure the ignition switch is off so you do not blow a fuse between tests.

To check the fuel gauge unplug the sending unit at the tank. (May be easier said than done) and connect the two wires together. Then turn on the ignition switch to run. The gauge should peg. If it does then the problem is with the sending unit in the tank.

If it doesn't peg, turn off the ignition switch, ground out the colored wire to the sending unit to some bare metal on the chassis. Then turn on the ignition switch in run. The gauge should peg. If it does, there is a problem with the ground wire to the sending unit.

If it doesn't peg: Go inside the cab, disconnect the Fuel tank selector switch and jump the orange wire to the blue wire and the green/Red wire in turn. Does the gauge work? If so replace the selector switch. If it does not work. Ground out the orange wire to dash metal. The gauge should peg. If it does, then the problem is in the wiring between the selector switch and sending unit. If it does not peg then the gauge, the instrument cluster or wiring to the gauge is bad.


Since it affects both tanks the same way. I'd start at the selector switch and work backwards to the sending units. The odds of both sending units going bad at the same time are remote. (BUT it can happen) as well as the grounds to the sending units.

A non functioning fuel gauge due to cluster rot? Very good possibility as well...