1966 dart problems, help

Sounds like someone has been messing with the charging system. Stop driving the car and sort out whats been done and how to fix it. If there are three wires near the alternator, a green, blue and heavy black, it sounds like someone converted it to a dual field alternator - the 70 and up style. Does your car use points or have the mopar electronic ignition on it ? Usually when upgraded to the electronic ignition most people switch to the dual field alternator too. Your voltage reading is too high, it should be about 15 to 15.5 volts when the charging system is working "right".

Good luck with it.