[BenTwombly]

Bulb Failure Warning Indicator Light is Illuminated. It is the N7 "Lampenkontrollgerät". The warning (idiot) light in the instrument cluster on the right hand side, and next to the ABS warning indicator. It looks like a cartoon of an upside down “idea” light bulb.

 

[BenTwombly]

Bulb failure indicator diagnosis procedure as a summary and consensus from this and other forums.

You can narrow the diagnosis in a few easy steps.

Refrain from having your foot on the brake pedal during the first part of this short test.

(1) Turn on the ignition to position 2 (run) but not to 3 (start). All the warning lamps will light (turn on) as a 'bulb check' before the engine is started (as soon as the engine starts they all go out). If a warning light does not illuminate, the light is off, there is something not right, perhaps a burned bulb. Replace the bulb and try again.

(2) Start the engine. All the warning lights should go out. Foot off the brakes. Leave engine running & transmission in P (Park). Observe if a warning light is on. If all are off, go to the next step.

(3) Turn on the parking lamps. If a park lamp or tail light is out, as soon as you turn on the parking lamps that warning lamp will come on and stay on while the circuit is energized. A walk around the car will tell you which is out.

(4) Turn on the headlamps. If the bulb remains unlit (engine running), then comes on when the headlights are turned on, then it it a headlamp bulb. OK so far? Leave the engine on.

(5) Depress the brake pedal. If the warning lamp comes on, it is one of the brake lights. Also, the thing about the bulb failure light & brake lights is different than the other circuits. If a brake lamp bulb has failed the lamp REMAINS LIT, even with your foot OFF the brake pedal.

When you shut off the ignition the bulb failure circuit resets itself.

Also, if that bulb light stays on during the day (no lights on), one of the brake lights is out.

If you have a loose connector somewhere; a bump on the road may translate to a jiggling of the connection. Start with the easy stuff like the tail lights since they are a snap to remove and check.

Turn on your headlights and either go to the corner of the car and push on the quarter panel and watch to see if the lights flicker on that side, or if possible, see if the dash light comes on.

Another slightly easier but more time-consuming is to have a friend follow you as you drive over bumps, watching to see if any lights flicker.

The license plate light is commonly overlooked.

In one case: “There is a Light Control Module under the hood and the solder joints in it get cold and lose their connectivity. After going around and around on this one for over a year I went to this little box, resoldered all the little connector pins and for the first time in my relationship with this car the (warning) light is out.”

In one case: “Also be sure to use bulbs of correct wattage. I once changed the front parking lights and instead of 4w put in 2w bulbs (in pair). I didn't pay attention to that detail when I bought them, as they were looking exactly the same. So, the fault indicator was still on. I spent the next couple of hours checking every bulb, fuse, wiring, etc... Then I noticed that little inscription (2W) on the bulb...”

One advises: “The light bulb controller will always compare the Ohm in one part of a pair with the other, and react if the values differ to much. So it will compare your left front parking light with your right one. And your left hind blinker with your right, and so on. If you have a bulb that is about to go zulu, the resistance in it will change, and the light go on. Or if the wiring to a bulb is failing. If both bulbs are defect, the light will not shine. The difference in resistance will be zero.”

One advises: ”Always change bulbs in pairs. Never use two different bulbs in a pair. They must match exactly, and should have the same producer.”

One advises: ”If you replaced just one bulb recently then you will need to replace the other one too. A. Something I heard but more common sense than truth."

One advises: “You need to buy only mercedes benz bulbs not cheap bulbs from pep boys coz there is an extra resistance built into the benz bulb. A. Hogwash as far as I know, but change em in pairs. See above."

One advises: “It lights up to warn you of impending bulb failure. A. Most likely true.”

It's a trail and error process.

 

[MBZER]

Good stuff Ben.Been going through this exact ordeal for some time now.Fixed it...& now the washer light has taken the brake lights place.Its like the dash lights just hate being in the dark.

 

[BenTwombly]

Hey Thanks MBZER. I don't know why I keep writing this stuff down and sharing it with everyone, perhaps it's because it helps me understand it myself. Meanwhile I think the most useful thing we can do is to provide a valuable service to someone who has logged in looking for a way to solve a very real problem they are having. If we solve it, it is my hope they will return and eventually bring value back to us all.

And a note to my procedure above. When the key is in position 2 (run) and the engine not running, not all the lights come on as I had described above.

Meanwhile. I used the procedure to find that my brake light bulbs are the problem. I used an ohm meter to check the bulbs and they are fine. Now I've gotta find what is next in the steps. I think I'll replace the bulbs just to be sure, and then try again.

 

[MBZER]

Ya post this stuff coz YOUR a Benz ENTHUSIAST & a nice guy.

Checking the center brake light can be exausting...hit the pedal...run around the back...see if its on...very frustrating.

 

[jimbo51]

MBZER,
Wanna review that procedure before posting it on the DIY thread? I've been using it and I'm up to my sixth bulb - can't all be duds ;-)

 

[BenTwombly]

What have you narrowed it down to? Which bulbs are you replacing? Are you replacing them in pairs? Do you have any towing cables, accessories, aftermarket things or any such in the circuit?

 

[BenTwombly]

OK, I've taken my own tests and now I am finding the Bulb Warning Indicator comes on all the time after I touch the brakes. This tells me it is the brake lights. I replaced both the brake light bulbs with matched pairs, twice. No joy.

Then I finally realized the center light is part of it too (Thanks MBZER) and I replaced the who set of three, twice. Still no joy.

So I go rummaging around the wires and guess what? Somebody cut the left rear brake light wire (black with red stripe) and left it hanging (see photo below). Then they jumper the left brake light bulb wire to the right rear brake light bulb wire (red wire) so it would come on. Bizarre. Just goes to show you can never predict what someone has done before. I removed the aftermarket jumper. Spliced in a short piece (with solder). And JOY. No Bulb Warning Indicator when I press the brakes.

 

[MBZER]

I replaced all the bulbs in the trunk..that worked...hada lotta different bulbs from every where.

Ok Ben....If 1,2, or all 3 of the fog lights blew...would that little stinker of a dash warning light come on?
How about if the daytime (EURO) bulb in the headlight blew?
Would it light even if you don't use the fogs or the running lights w/out the headlights?
Didja exhaust out checking the center rear brake bulb?

HAHAHHAHAHAHHAAHHAH
(prolly found a better way...huh..?)


Think we have trouble...what about this poor sap?

 

[MBL87560SEC]

Sorry to Hijack this Ben, but I believe this has already been done......

So MBZER, nice pic of the '73 Porsche 911 nose. I had some of those hold-downs on a 1963 3.8 E-Type coupe I had nearly 40 years ago. Had 'em mounted vertically just between the back of the front wheel arch and the vertical door seam. Looked great!

Thanks for the memories. [] MBL

Selling that car got me to San Francisco in the summer of 1969... Road trip extrodinaire!! []

 

[MBZER]

!!!!!...OOh My DOG !!!...."summer of 69' "
Now...those were the daze !!!!
Kinda miss the good 'ol times...back then I was happy with my beat u^p,in primmer,V-dubb !!Ripped seats..reversed rims..dents here & there..piss poor heater,but man...I sure loved the wreck at the time.
& I never worried about scratches or wax or some guy ripping it off.
No..it wasn't covererd in Flowers

HAHAHHAHHA..But I did think about it.

Like R.Reagan's question..."Are you better off now then ya was back then?"
Interesting question...guesss I'd have to answer ."Yes & NO"...(that should cover it)

 

[BenTwombly]

Dear 483952:

Yes, I know this has been done. I have referenced this fact in my first line. I declared it as a summary of current searching. I have added additional value by cleaning it up and adding a few bits I had found on other forums. Adding value to the forum with each posting is something each of us should seek to do!

The reason for doing this is that I tried the procedures and found they did not identify the problem. So I dug a little deeper, cleaned up the procedure and discovered although the procedure is better, it still did not identify the problem. Then I stopped searching the forum and started searching the wiring ... and found the problem. It is discussed above. I hope you-all have found, or will find, this useful in some way.

Ben

 

[BenTwombly]

Hey MBZER: The way I solved the "running to see the light on" problem is I removed the cover on the center light to check the bulb wattage and brand and then just left it off so I could see it come on. Very handy. For the actual brake lights, I parked in front of a store glass window facing away and looked in my rearview mirror to watch the brake lights come on. But yes, it is handy to have someone around to press that pedal. Thanks. --Ben

 

[janos_z]

here i come again with my gordian knot approach, but whenever my "bulb out" light comes on, i just follow two steps:

1) turn on all the lights, including fogs and hazards; then do a walkaround and look for any lights out.

if all looks well:

2) park in front of store window or truck with a shiny grille or other reflective surface and press on brakes to see which brake light is out.

this has worked for me every time. of course, this wouldn't have detected funky wiring, but it sounds like there's no shortcut to diagnosing a prior owner's, um, creativity...

by the way, i am a big fan of replacing bulbs in pairs. not only do you ensure that the car's lights will be equally bright on both sides, but you also minimize having to drive around with burnt out lights and getting ticketed for it...

 

[MBZER]

Hey MBZER: The way I solved the "running to see the light on" problem is I removed the cover on the center light to check the bulb wattage and brand and then just left it off so I could see it come on. Very handy. For the actual brake lights, I parked in front of a store glass window facing away and looked in my rearview mirror to watch the brake lights come on. But yes, it is handy to have someone around to press that pedal. Thanks. --Ben

Gee..thx guys...Guess I'm gunna have to tell ya when I'am just "Ducking the Fog" & when I'm truly serious..(< rare @ bezt)

HAHAHHAHAHAHAHAHAHAH