You said the ignition switch is "hanging". I assume this means it isn't grounded to the dash. Try grounding the switch housing to see if this makes any difference. If that doesn't change anything, disconnect all of the non-stock wiring you installed for the MSD. This is just for trouble-shooting purposes so you can narrow down the actual location of the problem. Is there any other non-stock wiring of any kind installed on the car?
I just thought of something else. Are you still running the original 1965 type alternator with an external regulator?