1973 Duster charging issue

If there was another wire added to one of the field terminals on the alternator it would have to be with the dark blue wire. That is switched 12 volts. Probably just the easiest spot for the factory to tap in something like that auxilary choke heater added in 73.
Might have been for those models with their ignition module on the right inner fender too. Anyway.. the isolated field alternator has 2 field terminals and each requires only 1 wire, dark blue and green. Hope this helps.