With Ohm meter you can check the alternator field terminal and see if you have 0 ohm short, or read some ohms. The rotor winding is the resistance in the field circuit. I am not sure how a ground in the regulator would damage the green wire as it would not force a high current on green wire. It would be 0 volts and low no output on alternator. To melt the green field wire it had to carry full voltage to ground to generate the current flow to melt insulation. Either rotor is shorted, the terminal insulator is broken/ground out, or the green wire had damage insulation that shorted to ground, but you said it was a tape wrapped wire, so probably not the issue.