It can be done but will require some work.
The gauge guts would need to be changed out and a way to switch off power to it when car is off (might cause an excessive engine off current drain).
The older Mopars (think older muscle cars) all current, except for starter) goes through the ammeter. The ammeters FMJ’s used are shunted so not all power goes through them – which is a much better design – but to most people, the gauge doesn’t tell them much.
I prefer the volt gauge system better – but that might be because I use a volt gauge a lot for automotive testing purposes. Some might argue the volt gauge doesn’t tell them much either – but I’ll step out of that argument and watch from the sideline.
I have a couple of F and M ammeters that I would love to pay someone else to convert for me. I know someone who does a lot of gauge work for ’66-67 Chargers, that would do it. The big thing is I just need to get off my butt and get-r-done.
Note: the ’66-67 Charger gauges are unique in the fact the gauge face is electroluminescent (the backlighting is attached to the metal gauge backing with a black sticker placed on top so it glows through the sticker) and gauge dials are miniature light sticks. A very cool setup - especially at night.
BudW