More Dumb electrical stuff- cold weather related?

So this morning I get into the white car (1987 325e) and the battery's dead, great, of course this crap happens when I have a customer waiting. I luckily got mr. damp weather car started (my car, 1988 325is) and put wife'ies car on charge and went to work. When I got back I noticed the OBC on before I put the key in the slot, Dam, more shit to worry about!

I put a battery isolator on the negative post and told her about her new duties everytime she starts and stops the car for any length of time. SO, I'm wondering if the cold froze some relay or what could have gone south on me.

I'll sit down with the ETM later and see what is in that circuit that might give me a condition that would leave the OBC (and anything else on that fuse) on after the car is shut down.

Thoughts, ideas anyone?

Thanks, Rick

It might be time for a new ignition switch, but my first guess would be a relay.