Thanks, Donnie.
Actually, after going to the obvious locations first: passenger footwell (wire harness recall location) and the battery area, I found a poorly installed cellphone harness, installed when the car was new, had shorted against the sheetmetal under the passenger-side carpeting. This caused the following bizarre glitches:

dome lights in rear passenger area on at odd times, regardless of switch settings.

radio would shut itself off when braking! (pressure from shifting carpeting)

and of course battery drained to ineffectiveness.

found phone harness hot lead wired direct to battery (very stupid), and another lead soldered to #1 fuse (???)

I hacked everything related to the phone out of the car.

I can't believe I found the problem so quickly...weekend salvaged.

Once again, sometimes things are not what you expect!

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1995 MB E320 Wagon
2001 BMW 530i
2007 MINI Cooper S (!)