...else.  Perfect example I reconditioned a spare fuel tank I had.  First I had it professionally cleaned a local radiator shop.  when I got it back, it looked fantastic, but there was a lot of exposed metal on the outside.   I didn't want it to rust from the outside so I primed it, painted it, and then put a coating of truck bed liner on the outside.  Got the tank installed the other day and apparently I sealed the tank to well.  There was now no metal to metal contact to compete the circuit for the sending unit. It was a simple fix I added a ground that ties the flange of the tank to the frame and my gauge now works again.