[Bill G]

You don't want to adjust the third brush until you have checked all the connections. With any bad connection in the battery and charging circuit, the resistance increases which causes the generator to think it needs to up its output to compensate, which creates the situation you have. The path to check include:

(a) both battery posts Make sure clean and tight
(b) the connection at the starter coming from the battery. Check for good ground on the ground side of the battery
(c) if you have a fuse. check for bad connections. In fact for any wiring check for discoloration caused by the connection getting hot
(d) the connection at the cut-out on the generator
(e) either or both connections behind the black cover on the junction box on the firewall
(f) either or both connections on the back of the ammeter behind the instrument panel.

Any one of these points can become bad due to bad solder joints on the terminal ends or bad crimp-on connectors. At any rate, the above path is the charging circuit where bad connections can cause the generator to work. Once all the connections have been checked and double-checked, the over charging problem will be solved. Then you can adjust your third brush.