Hey Everyone,

I am new here and am having a bit of a problem. I recently bought a 1988 F150 4X4 in which the fuel gauge does not work. I have done extensive troubleshooting, and have determined that it is something from the fuel selector switch back (dual tanks). With gas in the tanks, the gauge shows empty no matter which tank I have selected. I have taken the gauge cluster out and tested the gauge, and know that the gauge itself works. If I disconnect the fuel tank selector switch, the gauge goes all the way up as expected. If I jump the wires between the front sending unit or rear sending unit and the gauge, still shows empty. I do notice that when I flip the switch I see the gauge move very slightly. So...are the sending units (floats) the only other things I can assume could be wrong? I know if the wire is shorting somewhere, this obviously could also cause the problem. Does any of the wiring for the in tank pumps effect the sending units (eg. the ground) or are these stand alone units? How likely is it for these sending units to fail? It seems a bit strange for 2 of them to fail. Also, What is the easiest way to get at the sending units, dropping the tanks, or removing the bed?

Thanks alot,
Mike

 

It's not that unusual. I have the same problem.

 

What do you mean by "jump"? Short to ground? That's no test since you obviously already have that. What happens if you unplug the tank connectors?

No, it COULD be the wiring, but the level senders are the most likely & common failure point.

Yes, the level senders are in the tanks attached to the pumps wired thru the same connectors.

Very, after 19 years. The truck is almost an antique in most states.

Probably the bed, for a pickup, but click my signature link & look thru the EFI Fuel Pump album. Yours is somewhat different (low-pressure in-tank pumps), but still similar enough for those pics to be helpful. This one will be, too.

 

Thank you both for the help. Steve, by "jump" I meant that I crossed the wire direct to the gauge with the one to the sending unit in the tank. By doing this I eliminated any possiblilty that the switch was causing the problem. I had thought about pulling the wires off of the sending units directly, however there seemed to be no way to get to the wire without dropping the takins or removing the bed as they are on the top of the tanks. If I am wrong here, please let me know. That could potentially save a lot of time and aggravation. Thanks again, Mike.

 

It's not that hard to release the connector from the top of the tank, even with the bed & tank in-place. As this pic shows, it's recessed & pointing forward, just behind the lines.



The connector is just like this one.



A trick we use on Broncos is shown in these photos, but I doubt you'd want to do that to a pickup.