If someone can give me a line to a current diagram, I can help you better, but here's how these things work, and I doubt that it's your alternator.

From the alternator, one wire (usually green) goes to the regulator. On these '70 and later systems, this green wire CONTROLLS THE GROUND so to speak through the regulator. That is, the lower the battey voltage on the sense lead--the other lead going to the key on the regulator--the lower this ground is pulled, making the rotor (brushes) draw more current and causing heavier charging.

The rotor (brushes) gets it's voltge right from "ignition run" usually the blue lead going right from the ign switch to one brush. It does not matte which brush these two leads are connected to.

One way to quick check the alternator, is simply pull (green?) wire going to the regulator. The alternator should NOT charge at this time. Using a clip lead, temporarily GROUND the exposed alternator terminal. This should (at a fairly fast idle) cause increased voltage at the battery and "full tilt" charging.

The "sense" lead to the regulator is fed from the ignition switch. THIS POINT MUST BE very close to battery voltage AT ALL TIMES. Follow this lead back to the key, and ESPECIALLY check this during running to be close to battery voltage. This means the connection at the regualator, the firewall connector, the connector at the ign switch, and the switch itself. On the "hot" (battery) side of the ign switch, FOLLOW IT if it's lower than "battery." Same thing--ign switch connector, firewall connector, and on back to battery positive.

One quick way to find out, is take an accurate voltmeter, and put one probe on the regulator ign terminal, (while running and charging, 'cruise') and the other probe on battery POSITIVE post. THIS VOLTAGE should be VERY low--the lower the better, and CERTAINLY below .5 (one HALF of a volt)

Same deal with your regulator ground. Stab one proble on the regulator CASE, and the other directly on the battery NEGATIVE terminal, again, while simulating 'cruise' charging conditions. AGAIN this voltage should be VERY low, less than 1/2 volt.

Once you get these two conditions met, and about the first thing I'd check is the aforementioned firewall connector and ignition switch and connector, if it STILL overcharges, then change the regulator.