Hi again Jay. I have an ET degree, and 30 years experience.
You have a grounded wire, between the gauge and the tank.
[ or someone before you reversed some wires somewhere.] May be easier to replace those two wires.
You do not need thick heavy wires, just nice strong insulation.
The gauge, thinks the tank is full, because, all the current is flowing to ground [-].
if questions tom granger c ell 410 627 05504.
On my sea hunt I had problems with my gas gauge, my son, an electrician found out the crimped connectors were not done right, one wire Pulled right out of the connector.