RodGuyinCo,
Welcome to the Stovebolt. I am going to take a wild stab at this and say it is the wire that was once connected to a polarity reversing switch. I sure didn't think they were around in '51, but maybe someone swapped distributors. Try attaching that loose wire to a good ground and see what happens. If the engine explodes and burns down the neighborhood, I will plead the 5th!
Stuart
