[Sean Marconette]

How old are the ignition wires? Dumb question, but wires played heck with my data acquisition system. New wires solved the problem. My old wires were only 2 years old. I also was told to install a RFI filter which is a gloried capacitor.
With what you have described, it sounds like a ground issue.
Is the engine grounded to the frame, and the battery grounded to the frame. Is the ground sufficient for the load? Is the polarity correct to the crank trigger for the MSD?

As Joe described, or I am reading into where he is headed. Disconnect everything that takes or makes power, start the car and check and see if the problem goes away. Then add One device at a time.

Sean