Some additional questions on the gauge, for an original two terminal gauge, should there be any internal ground connection for either terminal? I'm guessing not, but I've got continuity between the battery terminal and the gauge case when testing with a multimeter.
I see some of the replacement gauges use three terminals with one for ground, but is that for the light and not for gauge itself? Curious if the newer ones are wired differently. Also the backlighting must be internal (no longer plugging in the socket)?