Or, perhaps, the rear fog light is really an adaptive brake light.
BMW disables the rear for light switch in the North American E9x. But that's easy to un-do.
As for whether the E39 has any form of adaptive brake lighting, I still can't find that out. It doesn't seem to have extra bulbs that also act as rear fog lights overseas, though.
I did just stumble over this site, www.bmwtips.com, which didn't tell me that but has a lot of good stuff (not exclusively for the E39 either...)
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