I have the same problem in my 300TE. I am going to the junkyard next weekend to grab one of these units to see if it resolves it. My warning light only comes on when I turn on the headlights too. As said above, it is the long black one. There should be short ones and a long one...hard to miss.

Alternatively, you could always pull it out and check inside the box for bad solder joints. I did this to my Multi-Purpose Relay (The smaller one) and it fixed my wiper problems.

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2016 Monsoon Gray Audi Allroad - 21k
2008 Black Mercedes E350 4Matic Sport - 131k
2014 Jeep Wranger Unlimited Sahara - 62k
2003 Gray Mercedes ML350 - 122k

Thanks. But I think it has to be the license plate lights/bulbs, because if I take both out, no light, but no "bulb out" indicator either! So if the module was bad, I would think I would still get the "bulb out" indicator to light.

As I indicated above, it only comes on with either parking or head lights. If I remove the license plate bulbs, all the other outside lights work fine and no indicator light.

The replacement bulbs appear to be identical to the original, but I guess I can always run by the stealer and pick up a bulb to eliminate that as the cause.
Regards,
Jerry

Is the boot (Trunk) light included in the fault indication? Is the fact that there is no fuse for the fog lights another condition that will indicate a fault?

You have found the cause...

...the metal rails inside the rear lamp housings that hold the bulbs in place vibrate loose over time. When that happens, there is a loss of "ground", barely visible as a slightly dim bulb here and there, but perceptible by the lamp indicator system as increased resistance.

When you went about inspecting the bulbs, you had reseated the rails by simply reinserting the bulbs firmly in their sockets. That restored a good ground connection, and all was well according to the system.

This one took months for me to solve...

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2009 ML350 (106K) - Family vehicle
2001 CLK430 Cabriolet (80K) - Wife's car
2005 BMW 645CI (138K) - My daily driver
2016 Mustang (32K) - Daughter's car

This post is only for Solidarity.

Yeah, I've been there too. For some reason, the cars I tend to dig are models known for (shall we say) "whimsical" electrical systems. My W126 is the car whose electrical system I can trust, at least; my Saab and my Cherokee, not so much.

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'88 300SE | Midnight Blue | 237k
'09 Subaru Impreza | red | 0k

I was getting bulb out indicator on the dash, and only after doing all the head scratching, and pulling connectors in pairs, cleaning up the fuses, AND replacing the bulb out module with a spare I had kicking around... clued in here and LICENSE plate lights DING! Replaced it and problem went away.

Until today. Now, I'm getting same symptom as original poster. As soon as the car is started (light switch position = OFF, car parked) I get the indicator bulb on the dash. No lights are supposed to be on, how is this possible?

First thing that comes to mind is put the original bulb indicator module back in and see if it goes away. I'll do that tonight.

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Cheers!
Scott McPhee

1987 300D

I re-read the thread... the OP says failure indicator comes on soon as starting the car... same as me.
Then says adjusting the metal bits in a rear light cluster solved it. But none of these lights are "on" when the car is started.

Does this mean:
1. the bulb failure module "reads" some lights even before they are being used? Maybe ones in the rear (where a driver can't really see the problem while driving, as he could with, say a headlamp out.)

2. the bulb failure module remembers or "latches" the failure, after using the light and module notices an outage of an important bulb, say, a brake light bulb, and doesn't let you forget until the problem is resolved?

At least one of these has to be true, and possibly both. If after starting the car and you haven't used any lights yet for the drive cycle, and you get a failure indicator. ...Right?


Thanks!

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Cheers!
Scott McPhee

1987 300D

I found this in a related thread:

Same car as me, too!


So Sixtoes says it latches, but only for brake lights. It sounds as if the latch would be cleared when the key goes off, and not re-latch until brake is used again. ... or detected intermittent... So does this mean it can detect even if the light is not used, all by "itself"? Maybe. And that supports the OP's post and my observation of when it comes on, and what fixed the OP's problem.

This makes me want to check my brake lights, before suspecting and yanking the bulb failure module itself.

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Cheers!
Scott McPhee

1987 300D

I was ticketed for my rear tailight bulb being out. However when I looked to replace it in the upper bulb space it looked like the light bulb assembly was never installed in this space.There was a flat cover on it and it would not accept one of the bulb assembles that are usually used. I have enclosed a picture. Do all E300's the same? If not can anyone clue me in on this phenomenom? Thanks

Attached Thumbnails

 

I had a pesky light failure indicator for several weeks in my 560. It turned out that there were cracked solder joints inside the bulb monitor module. All I had to do was open it up and re-solder the joints.

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-tp


1990 300SE "Corinne"- 145k daily driver - street modified differential - PARTING OUT OR SELLING SOON - PORTLAND OR. AREA - PM ME FOR DETAILS
1988 560SEL "Gunther"- 190K passes anything except a gas station
1997 S420 - 265k just bought it with a rebuilt trans. Lovely condition