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On my 72, there was not a nut or anything to hold the connecor on. And there was 1 'prong' that was longer than the rest - I think it was the center one on the drivers side.
I am not sure about your 73 but some GM models use a little colored plastic nut that kind of pressed on the long shaft to hold the connector on.
I don't remember the last time I saw the retaining nut but the nut also covered the stud because the stud is HOT. I cut the stud off so it doesn't come in contact with ground and cause a short or fire.