As previously mentioned the green wire provides a variable ground to one of the two field terminals on the alternator.
If that wire is grounded it will cause an overcharge.
The fact that you disconnected it and still had over charging points to the terminal on the alt being grounded as 67dart273 mentioned.
If you disconnect both field wires and measure resistance to the case of the alt I suspect you will find one with 0 to 0.5 ohm resistance and the other something greater than 2 ohms
