NorCal49er is right, pull the main wire off the center of the sending unit. When you ground it, the gauge should go to zero. In my case that test worked which meant the gauge was good. When I pulled the sending unit, I had to laugh. It was completely corroded and covered with old varnish.
I ended up pulling the tank and getting it boiled out, then getting a new sending unit from Jim Carter. The new unit ($32) was kind of a piece of junk made in Argentina. Really cheapo construction compared to the original unit, but it works. You can hook up the new sending unit to the gauge and test it before you install it. Comes with a new rubber gasket.
David Bush
