The above comments are correct. FYI, When the wire that runs from the tank to the guage is disconnected the guage will peg itself on the full side so a bad connection anywhere along the way will cause your problem. It sounds like your guage is OK, it's not getting the signal from the tank.
I have a similar problem. I've got a '70 Elky non-SS and when I fill it up with gas, the gas guage doesn't go all the way to the top even though I know the tank's full. Is the guage sticking or is the sender in the tank? Thanks!
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