You still running the ext regulator? Sounds like points are stuck inside the regulator. If you're getting 15+ volts, the alternator is working, the regulator is not controlling its output. With it running, try TAPPING on the regulator cover to unstick the points inside. I would go ahead and replace the regulator anyhow. When you unhook the pos battery cable and touch it back to the battery post do you get a large spark? If so, you have something drawing alot of current, could account for the overcharging.