I dont know if this will help you, but my guage read over full after it had been working fine and sat for a while and the wires to the sending looked ok.
It was driving me nuts because I had a newer Autometer fuel guage installed for years and it was allways working correctly.
I finally found that the ground wire to the sending unit tang had rusted so bad even though it still was attached to the sending unit , the ground on it was
NOT GOOD enough.
I cleaned up one of the metal outlet tubes on the sending unit with sandpaper, wound the ground around a few times and reattched the wire with a small mini hose clamp so it was on a
CLEAN ground on the sending unit itself.
Doug in AZ
My Old Monza now lives in Arizona with its newest owner.
The 90's just keep rollin' along........
1990 Chevrolet Silverado Regular Cab Long Bed 350 TBI V8 700R4 118K miles
1992 Pontiac Sunbird Coupe 2.0 OHC MPFI I4 TH125C 157k miles