Starter keeps turning over!

Well today i went out and drove to my friends house and when we were leaving her house i started my car and it started up but it made the sound like your trying to crank your car when its already started, and it wouldnt stop. i even took the key out of the ignition and in the off position and the engine shut off but the starter was still trying to turn over. It Went on for about 5 minutes while i was trying to pull off the battery cable untill it finally fried out and started to smoke. i have a 92 mustang gt and i have heard of something about the msd power wire and the voltage regulator might have something to do with it. is this the starter? relay?ignition switch?

I had the same problem shortly after I bought my '87 LX. TRy the soleniod, thats what fixed mine. I used an F-150 solenoid, not sure if there is any difference, its just what I had laying around.