I'd start by going through the factory service manuals and look for models (guess: 72 Fury) that started using shunt type ammeters. The shunts in those cars were part of the wiring harness, and in some GM, some Mopar, and "most Fords" the design made the ammeter quite "numb". That is, say you turn on your headlights, you had to REALLY look at the damn thing to see "if it moved." This can be changed by changing the shunt---the harness--but what that means is more wire length and more voltage drop
If you do this, at least do so in such a way as to to eliminate the bulkhead connector problem.
