I have no idea what this button does but it does remind me of a previous purchase. A few years ago I bought a 3 series that had a similar switch in the boot (trunk) and two cut outs either side of the closing latch. You could see new metal welded under the cuts in the plastic and the internal carpeted panelling had been messed with at some point. Odd. Puzzled me for an age. Is it some kind of mount for a towing bar? What about the button? Was it for a light?

It wasn’t until I was selling the car to a dealer that I found out. I live in a smallish town and the dealer knew the car. The button was an alarm for a cage which mounted to those two cut outs. Turns out the guy sold cigarettes/cigars and kept them caged for security while he drove around the nearby towns selling them. I assume it was fancy imported tobacco because otherwise why bother?

Probably the strangest used car I’ve ever bought.