My 1981 264 GLE keeps running when I turn off the ignition and remove the key - as though the key is still in position II.

It happens intermittently - only once a week or so - and has only happened about five times so far. The first few times I just waited a minute or two flicking the ignition key from 0 to I to II and back and it turned off (after a few flicks).

The most recent time, even flicking the switch would not do it - it stayed running for well over five minutes.

Details are a little sketchy (it was late at night and I was tired), but I'll do my best...

To stop the engine, I pulled the main fuel pump fuse, but the ignition power remained on (albeit without the engine running). The warning lights in the instrument panel were all still on, as were the daytime running lights and dash lights (clock, etc) - as if I had the ignition key in the II position ready to start it.

I tried flicking the key again. I then pulled the plug off the back of the ignition key switch (thinking the switch had stuck inside) - no change.

I pulled another fuse to stop the seat belt warning light, which was annoying me by this time. At that point, the instrument panel went dark and the lights turned off - but putting the fuse back in made them all light up again (obviously that fuse powers those lights and the seat belt warning).

Another fuse made a relay click off and on in the centre console (but didn't seem to affect anything else obvious).

With the fuses back in (but engine not running) I went back and flicked the ignition again, and hooray, the lights turned off. When it did I noticed an audible click of a relay in the centre console.

Not feeling safe enough, I pulled all the fuses before going inside for the night.

The next day I went chasing with a multi-meter. I was mainly looking for shorts in the fusebox area or loose fuse holders. I also checked the ignition key positions by testing for voltage on certain fuses. I did not discover anything unusual (though I didn't look very far I suppose).

My thoughts on the cause:
-It's not the ignition switch itself (because I tried pulling the plug off it).
-The relay in the centre console that normally clicks on when the ignition key is in position II is probably ok (not sticking) because I made it click on and off with one of the fuses (of course, I'm assuming that is the actual ignition relay - there was nothing else 'on' at the time that would involve another relay in the centre console I think).
-It seems heat related because it turns off itself after a while though it has happened after both long trips and short trips.

I'll experiment more with trying to turn the car off (it's becoming a game of sorts). Being intermittent makes it a long experiment though.

Anyone had this problem, or can share some insight on what electric circuits are involved with keeping the igition powered? I have the Hanyes manual and have been looking at the circuits, but there are lots of bits to eliminate and it's not easy to suss a problem when you can't make it happen on demand.

Cheers,
Andrew.