[DanEC]

It's possible that 5 gallons might not be enough to register.

I haven't had to work on my ERA's unit, but I've had to fiddle with various tank gage unit over the years to tweak the arm and float where it bottom out just a little off the floor of the tank. Did you look the float over carefully - any chance it's leaking and filling with gas?

The tank should be well grounded to the frame but maybe the gage sender is being isolated from the tank by the gasket. As I remember I had only a single wire hookup on the ERA. But I've got an old Plymouth that actually has a ground strap from the sender tube across the rubber connection hose and tied to the steel supply line. I think my Corvette sender may have a separate ground from the sender unit to the frame or harness. Might try connecting a ground wire to the sender unit steel and see if that helps any.