I had an old '68 pickup back when I was in High School. One day I pulled into my parking spot at the school, turned off the key and the motor kept running. Turned key on, turned key off, turned key on, turned key off, motor still ran like I was doing nothing. So I ended up putting it in 4th gear, holding the brake and popped the clutch, that killed it.
Later that evening, I investigated the cause of the problem and found it to be the key switch. No matter what position the key was in, the ignition system had power. The only thing that seemed to work on the key was the START position would engage the starter. Having to fix it that night, I identified and cut the wire coming out of the key switch and installed a toggle switch under the dash. So now, to start the truck, I would flip the toggle and then use the key to start it. To kill it, I would reach under the dash and flip the toggle switch.
One several occasions in the years following, I would forget the toggle switch and crank and crank and crank on the engine. Then I would remember the toggle switch. DUH!
