MY 1996 F150 TRUCK HAS DUEL TANKS. bOTH WORK BUT RECENTLY ONLY THE FRONT TANK REGISTERS A FUEL LEVEL ON THE GUAGE. WHEN SWITCHED TO THE REAR TANK, THE TRUCK STILL RUNS FINE BUT THE GUAGE GOES TO EMPTY EVEN IF I PUT GAS IN IT. THE FUSE LOOKS FINE AS FAR AS I CAN SEE. WHAT IS WRONG?