I guess we can close this one with a great big NEVER MIND; after having the trouble described above, I left things slightly disassembled in the garage to come in & check the Bentley and write out what's posted above. Went back out just now to button things up so my wife can drive it to work tomorrow, and find that the right front corner light was working again! Cool! So just for giggles, I plugged the left side back in, turn on the lights, and guess what; it works too! So I guess I answered my own question; the system must reset itself after a time with the ignition turned off. Switching it back on just now seems to have brought it back to full function. Go figure.

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2001 X5 Sport 3.0/5-speed
1998 318ti/5-speed
1988 735i/5-speed
1984 528e/5-speed (soon to be M20B25-powered 525i!)