Thanks to all who responded to my question about the malfunctioning check control unit on my 535i (indicating bad brake lights, license plate lights, and "rear lights") - Jim Cash is the lucky winner this time, the solution to the problem was easier than I ever imagined. There is a black plastic box near the trunk latch (behind the carpet panel) with two multi-pin connectors, merely removing and reinstalling the connectors got it working correctly. Apparently a few of the pins had oxidized over the years. When it warms up, I'm planning on packing them with dielectric grease for a permanent fix. (Froze my hands merely doing that, it's about 25F outside! I thought it was supposed to be warm outside this week!)

In testing it, I noticed that if you cycle the headlight switch a few times, sometimes the license plate light indicator will come on, so possibly a bad headlight switch can also cause this kind of problem (forget who suggested that one) but also I noticed that one of my license plate lights is cracked from the inside (there was no carpet when I bought the car) and slightly corroded so that may also be the problem.

For reference, I am NOT using Osram/Sylvania bulbs - I believe all the ones I have replaced have been with Wagner bulbs (what my local parts store carries) although I did look up the numbers in the cross-reference book and they are NOT 1147's - I forget the number, but it's 5 or 6 digits - apparently Wagner makes a special line of bulbs with tighter resistance spec's for these kinds of applications. They seem to work fine.

Perhaps this should be a FAQ entry (hint, hint) - I have relied on my printed-out copy of the FAQ as a service manual and it has served me better than any commercial manual, as it covers a lot of niggling little age-related problems that a regular shop manual wouldn't, but I had to go to the Digest for help on this one.

thanks again for all the replies.

nate
(now if I can get the service indicator to work, all my annoying blinky lights will be out!)

PS - another useful tip that I got (sorry, forget who mentioned this one as well) was that you can cancel the blinking "check" light below the SI by pushing the "test" button on the CC display - then if it starts blinking again, you know you have ANOTHER problem, and it's not the same old thing you already know about...

PPS - my backup lights are out AGAIN... I bought a new backup switch, and before I had a chance to install it, they started working - now they're out again - I think my car is posessed! Where does it screw into the tranny/shifter, anyway? I spent about 1 hr. looking for it, and didn't find it...

PPPS - another niggling little problem - sometimes my third brake light doesn't work, but it starts working again if I remove and reinstall the plastic cover. Makes it kinda hard to troubleshoot, and it never fails when the cover is off... don't really expect any help on this one, just whining...