I just bought a 2000 MC SS with the 3800 V6.All the lights, interior and exterior, dash,flicker when I turn the car off. I hear a clicking behind the glovebox. Occasionally, the headlights remain on as well. I got up this morning and the battery was dead, so it must have randomly activated. Any clues? Fried switch? Controller?

 

I moved your question over into this area. Hopefully you'll get a better response to your question.
I've never heard of this happening before unless someone did some custom wiring. Sounds like something is shorting out. Do you have any aftermarket electronics or electrical accessories that are not factory equipment?

 

My BCM went out on my "01 SS LE and had similar problems, but it was on start up, not shut down. Clicking, and flickering lighting. The BCM controls all lighting. The switches and light sensor tells the BCM what to do.
That's my guess.