single field to dual isolated field alt

RedFish is right, I was thinking maybe an overcharging situation was frying the Instrument panel Voltage Regulator??

I doubt thats the case. A modern solid state regulator should function with supplied voltage from 7 to 35. Over charging can fry about anything though.
I imagine some screwed up stuff in the instrument panel can kill the instrument voltage regulators and cause the overcharging too.
Without knowing what panel it is and a lot more details... who knows ?