all mopar of that vintage would be 5 volt gauges.
otherwise if you must have 12 volts you are better off buying an aftermarket gauge and changing the face plate.
Good info. I have tried SW aftermarket gauge (in fact I have 2, a 2" and a 21/16"), which is round. My gauges are rectangular, and the round "works" will not fit in my small rectangular slot (48 DeSoto cluster). Best of my knowledge, there are no aftermarket rectangular gauges?
When you say 5 volts? I do have a volt reducer (12 to 6) installed in my system for gauges and dash lights?
Jack