If I wanted to run a separate voltage gauge how would wire that in? I kinda like the cig light adapter idea I have a bluetooth in my edd that has that feature.
Wire the positive to the location you want to measure voltage, preferably a location that is disconnected with the key off.
There may be a terminal in the fusebox that's available on the 'accessory' feed. "Accessory" is everything not related to running the engine and is switched.
Sometimes there's an available connector or switched power terminal in other locations such as the wiper switch.
The cig lighter is certainly the easiest.
The last '75 I was looking at had the internally shunted ammeter and was wired like most standard option '72-74 as far as the main feeds went. @zkx14 car and he checked whether it had the ammeter connections were through the grommets here
But if Redfish says shunted ammeters came in during '75, I wouldn't doubt that. So as far the wire paths go, see what is on your car and how it matches up.
