W124 unknown bulb out?
 

The exterior lamp failure warning light is on in the dash in our 91 300TE. The strange thing is that I cannot figure out which light is out. The headlights, parking lights, license plate and rear lights are all on. To complicate the situation - this warning light is on as soon as I start the car, without turning the lights on.

Not familiar with what would cause this...anyone else have seen this?

Dome light? It might still be on by the time you start the car. Not sure how long the time delay is, but I think long enough to put on the seatbelt and give the key a twist. Slide the button to the 0 position, and see if it still comes on.

Sounds like the brake light, a lower or the high center mount.

to chime in... but there is a small bulb in the tail light... that one has caught me..

also license plate light....

it is not the obvious ones!

Don't forget to check the back up lights and left rear "fog (tail) light" too.

light out
 

Aamge 55,

If you have not located the bad light yet, consider this:

Check which system the warning lights on either side of the "bulb out" warning light address (I think one is "low washer fluid", do not remember the other) and make sure those systems are working OK. If not ... for example, if your washer fluid is low, it may be because someone replaced a burnt out bulb in your instrument cluster and mistakenly put the "bulb out" bulb in the wrong hole - if so, next time you have the cluster out you will need to switch those two bulbs.

No need asking how I know this can happen.

to add to what others have noted - the bulb out indicator can only the lights that are currently suppose to be on. So - if you start the car (without pushing the brake pedal or turning on the headlights) the lamp shouldn't be lit, period.

If it is - I would guess that KermitF is on to your problem - the MIL is for some other system.

If it is not on - press the brake pedal - does it come on then? If so, you know it is in the brake lights...

Skiier3_9, I agree with you, it should not be on. When I start the car, without it in gear, without turning any lights on, that warning light is on. This warning light should indicate which light is in use that is currently burnt out. So rear brakes, fogs wouldn't have triggered it.

As for KermitF's suggestion, we've had this car since new, so I am 99.9% sure nobody's been inside the instrument cluster to swap bulbs yet. Lee, the license plate lights have caught me too, couple of times at the inspection station. So that's the first place I look now.

Also - to head off another cause: I've heard that changing to lower wattage LED bulbs will cause this, but I don't have any. All the bulbs have been on the car for at least a couple of years, so it's not from a recent change.

I'm going to take a comprehensive look tomorrow. Maybe swap out each bulb one by one to see if I can isolate it. Thanks for all the suggestions so far.

The mystery continues.....

As far as I know ( and that's not much ), it could be a suspect connection between bulb/socket.
May as well check all the sockets when you're pulling bulbs anyway. ;)

If you didn't know, you are supposed to used the european wattage bulbs, not the domestic ones. How's your brakelight switch?

After going through each bulb, finding them all good. The warning light disappeared. Arrrrgh! It was after I checked the left rear set of light clusters it went away. Maybe it's like what Manny said - just a matter of seating it in the socket.

Nevertheless, it's off now. Still annoys me that I haven't found the cause.

Wd40
 

a tiny dab , on the contact points (clean) ,of each bulb [and clean contact
points of each socket]will make this annoying situation less likely in the future.

I have had problems with the contacts in the left rear tail light assembly too. I think it was corrosion, because when I took all the bulbs out and hit the contacts with some very fine grit sandpaper, it went away. Hasn't returned for about five years now.

To ressurect an old thread, I have the bulb lamp warning lot on only when I turn on the lights on my new to me W124 Cab. I had a license plate bulb out, traced it to a bad wire in the hinge of the trunk and thought that would do it.

The license plate lights are now on, and all the other lights seem to work, but I still get the lamp bulb warning when I turn on either running lights or headlights. What am I missing?
Regards,
Jerry

Check to be sure that they are all the proper wattage, it is in your owner's manual and molded into the tail-light bulb holder.

The side-lights in the tail-lights are notorious. It is an outside light system only, not inside lights, and as it comes on without the headlamps or foglamps on I would eliminate them.

Can also be the lamp/warning module itself, open the cover behind the fusebox and it is the longest plug-in module.

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.

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...

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.

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.

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!

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.

Another Taillight problem with 97 E300, Need it fixed Immediately
 

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

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.