I just fixed this very problem. MSD even states that "run on" is a common occurance in their manual. Stating that, "electric fans sometimes feed through to the ignition causing a small light inside to remain on telling the system to stay powered up". Put a 1A 100v diode in line and your problem is solved. If you don't have a manual I can email the proceedure to you with pics. I have an MSD 6A. If that's what you are running, let me know.
