84 GT alternator wire harness

[gunnylama]

So I understand harnessy three wire go, field, batt, choke, but I don't have a ground wire. When I cut into the rubber wire collector thing, there is a broken off wire in there where the thing connects to the stud with the nut. Is this the ground? This is a 84 GT and I installed a new 85 alternator wire harness which had a three wire plug not two like the 84. The 85 has a white/black wire that runs to the carb heat and up to the plug.[ATTACH]114597[ I cut off the 3 wire 85 plug and spliced the 84 plug in its place minus the white/black wire.