My rear tank's fuel gauge goes past full and stays there. I wish I had the magical always fuel tank, but unfortunately it does get emptied. So it looks like the tank selector valve works. The gauge reads accurately for the front tank, just not for the rear tank. Is there an easy way to tell if it is the sending unit or hopefully something much easier and cheaper to fix?

 

Sounds like you have done the research and it does sound like the sender unit has gone bad or a wire has come of the send unit.

 

Usually when the gauge pegs at full or overfull and stays there it means there is a ground wire that has come undone. Cheap and easy fix

 

I agree with F350_Hauler on the open circuit/undone ground wire. Hopefully you can find it pretty easily.

 

Mine is doing this right now. It's pegged ~1/4 tank past the Full mark. It started the last time I fueled up Saturday night. Is it typically the ground wire at the gauge, sending unit or is there a harness? Is there a wiring schematic for this?