76 dash in a 74 Dart?

I understand. 76 was very different

74 dash harness would have 2 very heavy gauge wires ( a red and a black ) attached directly onto the amp gauge. 76 has remote shunt design. So small copper traces attach that amp gauge just like the other gauges. Those copper traces cannot carry the full current so if installer did simply put those 2 large wires of a 74 harness in the round connector, that would explain fried traces to amp gauge.
Ahh I think you hit the nail on the head RedFish. I didn't notice the traces going to the ammeter were the ones I thought were rubbed off, they in fact vaporized. I've since done the ammeter bypass under the hood, but I never thought to look at under the dash wiring. I really only need the gas gauge and speedometer to work. So maybe I'll take your advice and wire the gas gauge directly with an aftermarket IVR. And slowly back away from the unknown monster under my dash...