A lot of voltage/current going through those 3 wires !!! Any slight looseness and/or corrosion results in resistance = heat. Common problem on a lot of bikes dating way back. (I've seen lot's of old Hondas and Yamahas with this problem).In the meantime I will now attack the 3 pin plug between the alternator and the regulator, which has been cooked. Very tempted to solder that. Very rare that I have had to unplug it.