Factory ammeter

I’m having an overcharging problem, I’m getting 16 volts out of the batt. Lug on the alternator, but 14.5 at the battery and starter relay. I have tried 3 regulators and 2 alternators no change. I’ve checked the green field wire and it’s fine between the alt and vr. Where do I go from here? It’s a 75 duster.