Brake Goes Light On, One Tail Light Goes Out
 

My 1994 E320 has a maddening gremlin in the tail lamps.

It began with the passenger-side side marker light. No matter what I do, I can't get the thing to illuminate. I disemboweled the passenger-side lamp, cleaned and tightened the fixtures, etc. No luck. However, the main tail light on the passenger side (same size) works fine.

So, trying to outsmart the system, I disconnected the green-and-white side-marker light wire, then ran a jumper wire from the green-and-black wire to main tail light terminal -- and got both bulbs working. Or so I thought.

Everything works fine until I step on the brakes. As soon as I do, the main tail light bulb on the DRIVER's side goes out -- and stays out. The dashboard warning light comes on, too. Meanwhile, my jumper-wired lights continue working fine. So do the brake lights and all the other exterior lamps.

Anyone have a suggestion? I need to pass state inspection in a couple of days ...

Thanks!

Check the grounds. It's always the grounds when it affects multiple bulbs (or systems).

Headlight relay
 

Behind the fuses under the screwed down cover is a long relay, when it starts to go it will give you such issues. It controls power to all the light. It is called a headlight relay or bulb out indicator relay. Usually the headlight part goes out first because of the draw on the board. When I got my 400E I had no indications of bulb out, but oops I had bulbs out so I replaced it with a part from a junkyard and bam it showed bulbs out. It also showed that someone had rewired the tail light probably because the indicator would not go out. I had to correctly rewire the passenger rear side marker light. about 2 and a half years out and it always works as it should. Hope my experience helps shed some light.

Thanks, I think I fixed it ...!
 

Thanks fellas ...

After I sent my post, I pulled the driver-side rear lamp and took it apart, looking for any visible problems. I really didn't see any, but now that I reinstalled it, all the tail lamps and brake lamps are working fine! Perhaps babymog was right, there may have been a ground fault that was corrected when I reassembled the lamp. I drove about 10 miles and, so far, nothing amiss.

But just in case Macdrone's idea is possible ... are you referring to the blocky relay that sits north of the under-the-hood fuse box, near the cowl? I replaced that bugger about two years ago -- it was the culprit in a lot of problems I had with turn signals. My turn signals would work fine a couple of times, then peter out. I'd reset the hazard switch and they'd work fine for awhile, then blink slowly, then cease altogether. Really weird: this happened only on hot humid days; they were fine in the winter. Anyway, I discovered on this forum the $75 relay that, once replaced, cured all those problems.

So ... for now ... I'm keeping my fingers crossed ...

Could also be a sign of sloppy body work. I can't count the number of times a body shop has screwed up the taillight wiring when replacing a panel.

Update on this peculiar problem
 

In my post yesterday, I claimed all was working well. And it was ... until last evening. I drove eight miles with the headlights on and no prob. After picking up a friend, I restarted the car, turned on the headlight switch and -- bang. I get the warning light on the dash as soon I stepped on the brake to put the car in reverse. Argh. But then I tried something different -- I shut down the car, restarted and, without headlights, all was fine. Then I turned on the headlights slowly -- one click at a time -- and my problem didn't reappear.

I should explain: My headlight switch has been a bit jerky lately -- feels like the detents are worn, and sometimes I have to exert more-than-usual force when turning it to get the headlights on. Plus, the pull-out feature for the driving lights no longer works ... it slides out and the driving lights illuminate, but won't remain in position.

So yesterday I finally discovered when the headlight switch goes just a shade too far in its clockwise rotation, it does something to the circuitry to cause the tail lamp problem (and warning light). Who'da thunk it?

Naturally, I'm now ordering a new headlight switch ....