I gotta a 1990 F150 and my fuel gauge is showing past full all the time. I did get a new fuel tank and fuel pump and the housing for the fuel pump so a new sender as well i believe. So what could it be?
Sounds like an open circuit. Disconnect the fuel sender wire and with a test light probe the wire with one end of the test light and the other end of the test light to ground. Your fuel gauge should start to move towards empty. If it doesn't, you may have an open in the wire or a bad fuel gauge.
Do the same thing with the ground wire for the fuel sender, only this time connect one end of the test light to battery voltage and prob the other end to the ground wire. If the test light doesn't light, you have an open in the circuit.
Be aware that if the vehicle has a metal fuel tank the ground may be a wire from the sending unit housing to the vehicle frame.
If your wiring passes the above tests, then you have a bad sending unit.
a fault in the wiring harness, or instrument cluster
It's either the gauge itself or the sending unit. Check circuits and grounds for each to find the problem. BC St answer is excellent.
