Problems with the sunroof drain can cause water ingress into the area of the BCM. Since the BCM controls all of the lighting, it makes sense that removing the fuse to the BCM stops the current drain.

It is puzzling that you mentioned a different BCM did not solve the problem... I would have recommended having the BCM software 're-flashed' as that can clear up inexplicable electrical gremlins....

Not sure that I have a recommendation for you.. if it were my car, I would trace the wire that feeds the power to the lighting on the steering wheel and disconnect it....

 

Oh, I would LOVE an original mini. There aren't a lot of them around Atlanta, GA.  Plus, I own this and this crazy problem is all that's wrong with it.  It almost has to be a stuck relay keeping power applied, just gotta find it.  I have the fuse bypassed for now and it runs awesome.

sell the BMW   MINI and buy a real classic mini.. later bc

I have a 2003 Cooper S.  Had the usual tube from the sunroof drains came loose and caused issues.  Cleaned it all up and fixed the tube.  Been fighting an issue for over a year now.  The steering wheel lights (volume + -, Cruise etc) stay on after the dome light fades out.  I tested the current draw and it only drops when I remove the 5A fuse for the BCM.  Granted, the BCM needs power but it's what's draining the battery.  If I remove the fuse, it will stay charged.  I have tried another BCM and replaced the Fuse panel.  I replaced the Fuse Panel because of the relays in the panel.  I can hear them click and though maybe one was stuck or something.

Nothing I have done has changed the problem.  It's not the BCM and it's not the Fuse Panel.  All the contacts are clean and no more leaks.  I feel that there must be a relay staying engaged that's causing the power to still be applied when I remove the key.....I just can't figure out which one.  Any ideas?  Thx