Overcharging?

That's not enough to go on. What have you tried or done so far? Is there any history that led up to this?

Your alternator will have two wires plugged in on the back. The blue one will have full system voltage when the ignition switch is on. The green wire must have less than the blue wire, but not 0 volts. If you do find 0 volts on the green wire, unplug it and see if it still overcharges. If it does, you have an alternator designed for a 1969 or older model. Those original alternators only had the one plug-in terminal for the blue wire. The terminal where the green wire would have gone is bolted right to the housing and is, in effect, for your newer model, shorted to ground. That will make it over-charge.

If you recently installed a newer replacement alternator, they often come with the terminal for the green wire grounded right at that terminal. They did that with a metal washer so it can be used on a '69 or older car. You need to replace that metal washer with the fiber one it came with. That must be used for 1970 and newer models.

If the system does stop charging when you unplug the green wire, either that wire is shorted to ground or the voltage regulator is shorted. Simply unplug the triangular-shaped connector on the voltage regulator. If that stops the system from over-charging, replace the regulator. For it to work properly, it must be bolted to the firewall. That bolt is one of its three connections.

Let me know if that helps.