Fuel Level Gauge 1985 truck

Having issues with fuel level gauge. Truck is an 1985 W150. gauge reads full all the time. pulled sender, cleaned, checked float. used ohm meter to check resistance in full and empty positions, all checked good. Changed gauge out with known good gauge from another truck. stumped......

Scraped or pinched wire somewhere along the frame??

check that voltage regulator on the back of the instrument panel circuit board...

if the voltage is high it will peg the gauge i think.

better yet if you can solder, you can install a solid state VR from $4 worth of parts form radio shack.
http://www.allpar.com/history/mopar/electrical2.html

If gauge reads past full with key on and with sender unplugged, the sending unit to gauge wire is shorted to ground.