This is an old tread, but I ended up here because "this" thing have happened to me too. Or my car to be more precise.
Anyway, when I got the car it showed more than 3/4 full tank, the next morning it was like 1/4 and it has been between there every since but not one time has it been the same as the day before. So, something has been going on.
I have had the instrument cluster out 4 times now, and after the third time, I turned on the ign. key, and a few seconds later I heard a "pling or a plong" from inside the instruments somewhere. Well, not that I hear like a cat, but it could very well have come from inside the fuel gauge. The fuel gauge did not work at all anymore, and not the temp gauge either.
Today I took the instrument cluster out the fourth time to fix the light in the speedometer that has caused me so much grief. And, took the fuel gauge out to measure it. Nothing about it in the shop manual, but I managed to set up a test circuit as per the book. The hand in the gauge had permanently gone to bed, and obviously liked to stay there.
Went online to look for new ones, Moparmall has it for $300 + whatever it was. Not for my wallet.
Opened the contraption, and the wire from the "I" connector to the built in voltage regulator is burned off, and it is a drop of metal on the outer housing, and it is black soot there. So, I wonder if the gauge have had a weakness there for all it's life, just that my turning things up and down and wherever and handling it several times has caused it to connect to the housing, and that was it.
Now, if I now had a piece of new wire, and two small rivets, I might be able to fix it. Long time since I were in the "instrument repairing business", many many years. Different kind of instruments too.
Bill