As Brad said likely the reg. 2 field terminal alt/flat 70 up style reg I am assuming. The batt is fully charged & this just happened out of the blue without a batt change? What I'm saying is you are not using the car to charge up a run down battery correct? Un plug the triangle reg terminal till you solve this as this "full fielded" condition is extremely damaging to the batt/terminals/bulkhead/any lights or accessories on as they ain't designed for 15+ volts even for brief periods of time and haveing the batt deep cycle a bit from being run down some ain't the best for a batt but is the lesser of 2 evils (by far). With reg connector plugged back for a moment in I would unplug the green field wire from the alt for a quick test & if it stops charging then I'd likely get a new flat reg.