Your float might not raise all the way to the top. Some times they get a pin hole leak. Mine reads MT with the key off and full with the key on. I ran new wiring but I think it's the sending unit.

1957 Chevy 10500 Fire Engine
1953 GMC 450 Pumper Tender
1957 Chevy 10500 Tandem Short Logger
1955 Second Series 3100
1957 3100 Shortbox
1957 Chevy 6500 Dump Truck
1957 Chevy 3800 1-Ton Flatbed
Lots of part trucks

Pix in Photobucket

"I haven't grown up, I just play with bigger trucks!"