I have a 89 f150 with 2 tanks ever sense I've had it the fuel gauge want work on front or back tank when you turn the switch on the fuel gauge jumps to full I know that's not right what could this be? I have checked all the fuses nothing seems wrong there
Have you check the Wire Connections at the tanks? They have a tendency to work loose and corrode, which in turn would cause your problem. Also with the age of the truck and if the in tank sending units have never been replaced they could be bad.