It you look at the back of your gauge you will see the metal plate. It must have good contact with the metal housing. If you cleaned up and repainted the housing make sure you sand off any paint where the gauge will mount so you have bare metal contact with the back or your gauge.

Image of back of gauge:
http://1954advance-design.com/Web%20images/1954%20fuel%20gauge/rear%20posts%20off.jpg


Dave from Northern Kentucky
My 54 3100