I bought the truck, didn't run, had a BAD fuel tank. Pulled the fuel tank, cleaned it out, replaced the pickup tube, runs fine. However, in the course of pulling the tank, I eliminated the auxiliary side fuel tank. There was a valve mounted on the frame and a number of hoses, wires, etc that enabled the drive to switch from one tank to the other. Now, the fuel gauge doesn't work. It is a 3 wire connector, that runs from just behind the cab to the tank. There are two sets of connectors, one is for the auxiliary tank, the other is for the main. I know that the sending unit is good, tested it with a meter while the tank was out, reads with a changing resistance as the float moves up and down. I had to clip the wires that fed the valve, but the sender wires are still there. Based on the wiring diagram, it seems like only one wire actually does anything to read the fuel level (Yellow w/Red tracer, see attached diagram). Not sure what to do next. Thoughts?
I would test this with a voltmeter with everything installed where it is supposed to be working. All measurements reference battery ground. Bk/Y should be battery voltage. Y/R should be a varying voltage depending on sender position. Bk should be 0 volts. Try those measurements at various places and see what you get.
No voltage anywhere.......
Nothing happens.....there is also no voltage present at the connector, key on engine off. I can't run it right now, no injectors are in the vehicle. Not sure if it needs to be running to send voltage to the sending unit. Lets just say that there is a problem with the wiring, and there is no power at the connector, could I pull KEY ON/ENGINE RUNNING power from somewhere else to simulate power to the black and yellow wire?
It looks like bk/y should be hot whenever the key is in on or start as it says in the diagram. Not just when the engine is running. Start there.
The Bk/Y wire has a fuse that is good and that same fuse powers the other cluster components. They all work right now. I wonder if something is broken within the dash. I did remove a couple items which were part of some 'Fleet Monitoring' system....
Found it. Bad connection at the fuel tank switch. The main and aux tank switch had some tape/goo on it from the previous owner. Looks like this was a problem before. Made a solid connection and now the gauge reads.