What does hanging loose mean? Loose from ground point or loose from relay. Yes big assumption that when measuring voltage he had ignition on. Not off.

If he has ground wire on frame of car and it measures 12V when hanging loose, he does have other bigger issues and I assume that would also mean the ground wire from battery is no longer attached to frame or battery since that would be a direct short across the battery and boom. But since he hung a separate ground wire to the relay and the car started, I don't think that is the case. Now, certainly it may be a works sometimes not other times relay, but..... he swapped in one.

So I guess we could ask, where do you ground your starter relay too (originally), since the safety switch was removed?