[Tommy]

To my simple mind, you are getting power to the ignition circuit when the key is in the run position, but not when it is in the start position. Sounds like a bad ignition switch to me. I'd put a voltmeter on the wire carrying power from the ignition switch to the MSD system and verify that it's getting power with the key in both the run and start positions. If it is, then you've exhausted my limited knowledge.