Found my dads original 1971 duster!

Sticks in my head that an ungrounded IP will cause the voltage regulator to send 12v to the gauges that are only supposed to see 5v. Maybe someone can confirm?

No saying for sure that the IP was ungrounded, just an idea I am tossing out there.

The other thing I seem to remember is the fuel gauge is supposed to be isolated from the structure. Can't put my finger on why or what, other than the stock Ralley cluster has the voltage regulator in the fuel gage. Could be if the guy that screwed you put the IP together, he might have put the fuel gauge in wrong and caused a short.