Hey everyone.. I have a 1997 7.3 f250 supercab longbed. I bought the truck in November but did not start driving it and fixing it up until January, I put some baby swamps injectors and a 6 position chip. Ok I have gotten pretty much all of the bugs out of it except for the fuel gauge which really has me frustrated. The truck has the regular dual tank setup.. When I bought it the PO said the fuel gauge just stopped working but it did switch tanks. I found it did not switch tanks, looked and looked for a selector valve but could only find it from ford for $500 hoping it would fix both problems, now it switches tanks but had no effect on the fuel gauge. The fuel gauge always stays way past full, doesnt matter if you unplug the cluster, unplug the selector switch, unplug the selector valve, dead battery, I have tried all these lol. I physicly took the lens of the cluster and put the gauge on 'E' but as soon as I put the cluster back in and turned the key on it went back to full. I am very sure it is not the senders because I have had senders go bad and usually only one goes bad and when it does go bad the needle does irregular things, doesnt just stay on full. I unplugged the selector valve and checked the the prongs with a tester light and the power does change as it is supposed to when you change the switch in the dash. I also have physicly checked all the wires to the senders, selector valve, selector switch, and cluster the only thing I have not taken apart Is the fuse panel.
Thank you

 

Have you tried Grounding the sender wire at the tank IIRC the lower the resistance the lower the fuel reading

 

Yeah if the tank is not connected good it will peg the gauge.