Msd 6al install. Now over charging

Couple of "first tests."

To see if the regulator at least has some control (and not that the alternator field is grounding) With the engine running "fast idle" disconnect first, the VR connector and make sure it stops charging--monitor battery voltage with a meter
Next to double check, same thing, disconnect the green wire at the alternator

Just what does it run up to, voltage? Monitor battery voltage, bring up RPM. If it is say, 16 or below, likely a problem in the harness or bad VR. If it goes above that, likely something grounding the field, which causes full output

Voltage tests: Turn key to "run" with engine stopped. Probe ballast and find "key" side, which should be full battery. Now measure from there to battery POS. You are hoping for a very low reading, more than .3V or so (3/10 of one volt) is voltage drop.

I sometimes recommend for a somewhat "easy" work around is to add a relay to relief stress on that circuit. The "run" circuit is a wire coming out of the bulkhead --usually dark blue-- that supplies underhood "run" loads---the alternator field, VR, ignition, electric choke if used, and smog doo dads if used. Cut that wire ;and use the firewall end to trigger a Bosch relay. Feed the relay power in contact with a fused/ breaker off the starter relay big stud. Connect the engine bay end of the cut wire to the switched output

Also check ground side for drop. With engine running fast idle, make this check first with all loads turned off, and again with lights, heater, etc running. Stab your meter into the top of the battery NEG post. Stab the other into the metal mount flange of the VR. You are hoping for almost zero, which is perfect. again, any reading there above a couple tenths means voltage drop. Improve grounding between block, body, and battery