What happened to my ignition system?

Hey Guys, this is my first time posting here. I hope I am in the right section. I've got a 69 Ford Mustang Mach One with a 377stroked Windsor engine equipped with 21 fused Haywire streetrod wire harness. A month ago I was driving to the supermarket and reached over to turn off the car and the car kept on running as though I didn't turn it off. The key was in the off position. So I went home and parked it. The car was still running, so I decided to remove the connector behind the ignition switch to shut the car off. I plugged it back in again and tried starting it up and wouldn't start. I got out of the car and opened the hood and noticed a strong smell, kind of like melted wires, coming from the starter solenoid mounted on the passenger side near the battery which is where the MSD was located also beneath the starter solenoid. So that is where I traced the smell and the MSD box was very hot to the touch. I replaced the ignition switch and starter solenoid... nothing the car didn't start. What caused the ignition system to keep on running after I put the key in the off position? What made the box blow out? This is my second box I have blown. It wasn't on there too long-maybe eleven months. Did I have to use a special diode to prevent spiking or arcing the ignition system. If so, why is it so sensitive? Anyhow, I think it shouldn't have blown. I performed the spark test according to MSD's instructions and even had someone test it in their MSD equipped vehicle and it wouldn't start his car up either. Right now, my car has sitting in my backyard for a month and need help deciding on which type of ignition system to purchase. I have looked at all the ignition systems I could think of from FBO to the DUI system from Tennessee. What I am after is a reliable and enhanced ignition system that will be able to burn the fuel as much as possible with causing detonation on a high performance engine . I would preferably want an ignition system that doesn't have to depend on a box. What ignition systems are you guys running? Have any of you had any bad experiences with MSD like the one I had? Any ideas and advice would be greatly appreciated, Thank you.

there is nothing wrong with the msd system Purple mustang, no better or worse than nothing else. it sounds like its not wired right. be sure you have a good ground, no loose wires, and how close do you have it to the exhaust? they dont like heat.

I've been using the HEI stand alone systems, got one of the cheapies (relative) from Summit and it seems to work fine. I've always thought the MSD systems to be a bit too sensitive for the street. I'm fairly sure you would have to have the car on a dyno to see any improvement over the HEI stand alone distributor. JMO but a lot of the race stuff should be left as that, race only. Eleven months of street use would equate to thousands of passes on the drag strip or a lot of laps on a circle track.