I think my sedan has a crossed wire somewhere in the driver's side tail light cluster.

When the headlights are off and I am not pressing the brake, all rear lights are off, as they should be. When I step on the brake, the proper, single light is illuminated on the right side, but two lights light up on the driver's side, the brake light and the nighttime running light. It's a six-panel cluster--on the driver's side, these lights are the outermost (brake light) and innermost (running light).

When the headlights are on, the "Bulb Failure" idiot light is activated in the dash, and only the right side lights are on. The left side cluster is dark. When I step on the brake, however, all of the proper lights come on. All together, I think that makes it four lights--the outermost and innermost panels in each cluster.

So, I think it's pretty obvious that, in the driver's side cluster, the brakelight and nighttime "running light" are linked together in a way that they're not supposed to be. Because of a crossed wire or some sort of contact between the circuits, the running light comes on during daytime braking, and the running light stays off while driving (not braking) at night.

I've taken the bulbs out of the cluster and made sure they get good contact. I've felt around and tried to see if I could get any loose wires out of the way, but I've found nothing that could be a culprit, and I have not been able to fix the problem.

Can I find a solution by doing little more than removing the plastic tail light cluster in the trunk and working from there, or will I have to get a bit more involved (unscrewing things) in order to find the short?
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'89 244 GL -- 105,XXX miles (see profile for info on car)

It's definitely a grounding problem, and the question is where is it?
Remove and clean the ground screw (black wire to body). Clean the terminal ring as well as the body sheet metal. Try that by itself, if no luck move on.
The outer bulb socket is a dual filament socket, the only one in the cluster. Should be black on the left- white on the right.
Remove and lightly sand or file the three tabs. Put in a new bulb. Inspect for white or grey corrosion on everything. White, yellowed, or cracked bulbs means water is getting in the taillight, and it's ALWAYS in the brake light, not the others. Darn things.
Clean the flex-circuit board on the taillight with a pencil eraser. Careful, they're a bit fragile. Need to see clean copper for it to work well.
Last, quite a few of these I've seen require the bulb holder to be loosened a hair from the full-clockwise position in order to make reliable contact. I figure it's just wear. Another thing I think contributes is that the spare tire bumps into the back of the left cluster, doesn't do it any favors.
Good luck!
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Rob Bareiss, New London CT ::: '87 244DL/M47- 230K, 88 744GLE- 220K, 82 245T-181K Also responsible for the care and feeding of: 88 745GLE, 231K, 87 244DL, 239K, 94 855GLT 189K

Another possibility could be you have an 1157 or 1156 bulb mixed up, ground causes lots of issues as well. if you have access to a test light try getting someone to assist you, remove all bulbs and test at the contacts with your assistant pressing the brake pedal. I t shouldn't take long to troubleshoot the source of the prob.
Good Luck
Ray
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keep the R's up!

Sounds like bad grounding of the cluster.

Colin.

1990 740SE B200E/M47, remote C/Locking.