I had an issue with a bad tumbler. I took the key out in the off position, but the ignition was still on overnight, cooking my coil and my Pertronix unit (not all bad since it convinced me to go back to points like Jesus did in the Bible, so to speak).
What I did to prevent this from happening again was to rewire the key illumination light to come on when the key is on and go off when the ignition is actually off. I just cut the wire going to the light and wired it to the "ignition on" lug on the switch..
