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Premium Member
'92 300TE 4matic 280,000miles, '92 300TE 4Matic 'Ice Blue Metalic' 101,000miles
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10,388 Posts
Discussion Starter #1
Last question for the night.....I've replaced every single bulb on the outside of the car, except for the headlights. I still have the exterior bulb indicator glowing on the dash panel. After replacing all the bulbs, the light went out....but idling a few minutes it came back on.

Are any of you familiar with this circuit; how much is involved and does it involve a computer and therefore throw a code, or is it just a simple measurement of one side voltage against the other?

Kevin
 

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Mercedes 300te
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1,970 Posts
What brand bulbs did you use? Sometimes the bulb can cause the problem... Just a thought..
 

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Premium Member
'92 300TE 4matic 280,000miles, '92 300TE 4Matic 'Ice Blue Metalic' 101,000miles
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10,388 Posts
Discussion Starter #3
Whatever NAPA had...probably Chinese. It's my understanding that one side's voltage is measured against the other....if there is a difference, the light comes on. Even Chinese bulbs should give very similar voltage readings if they are all new. I wished it was as simple as using German bulbs across the board. But even German bulbs are probably sourced out somewhere cheaper than Germany.

It was very frustrating to see the indicator light go off for a few minutes and then come back on.:(

Kevin
 

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W124 Moderator
86 190E 2.3L 16V, 2 95 320TE's, 02 S500
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12,745 Posts
Kevin,

Two things. A) check all the ground points (brown wire bundles) clean them and use some di-electric grease when re-mounting. B) what voltage are you getting at the battery with the car running?

Jayare
 

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Premium Member
'92 300TE 4matic 280,000miles, '92 300TE 4Matic 'Ice Blue Metalic' 101,000miles
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10,388 Posts
Discussion Starter #7
Kevin,

Two things. A) check all the ground points (brown wire bundles) clean them and use some di-electric grease when re-mounting. B) what voltage are you getting at the battery with the car running?

Jayare
Just under 14 and when I goose the idle, the reading goes up....I think the alt is fine. Yeah, that was my next idea too...start checking all the grounding points.

Kevin
 

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1993 MB 500E, 1965 MB 220b
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77 Posts
Kevin,

Two things. A) check all the ground points (brown wire bundles) clean them and use some di-electric grease when re-mounting. B) what voltage are you getting at the battery with the car running?

Jayare
Kevin, Jayare's suggestion (A) may be exactly what's affecting you. Prior to this year's State inspection (when else would something like this occur :confused:), my W124 car started exhibiting a similar behavior as yours; the indicator light would come on sporadically, yet all lights seemed to be functioning. I then noticed a rear tail light bulb malfunctioning (sometimes on/sometimes off). I removed the rear driver's side tail light cover. The bulb tested fine. The assembly's grounding point was the culprit. I did as Jayare suggests. Problem solved. In these types of situations, if the problem is not a bulb itself, it is usually a grounding point/wire that needs attention. Over time, a bit of moisture & corrosion will be enough to disrupt the circuit's completion to ground.
 

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Premium Member
'92 300TE 4matic 280,000miles, '92 300TE 4Matic 'Ice Blue Metalic' 101,000miles
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10,388 Posts
Discussion Starter #9
Kevin, Jayare's suggestion (A) may be exactly what's affecting you. Prior to this year's State inspection (when else would something like this occur :confused:), my W124 car started exhibiting a similar behavior as yours; the indicator light would come on sporadically, yet all lights seemed to be functioning. I then noticed a rear tail light bulb malfunctioning (sometimes on/sometimes off). I removed the rear driver's side tail light cover. The bulb tested fine. The assembly's grounding point was the culprit. I did as Jayare suggests. Problem solved. In these types of situations, if the problem is not a bulb itself, it is usually a grounding point/wire that needs attention. Over time, a bit of moisture & corrosion will be enough to disrupt the circuit's completion to ground.
Yeah, the license plate light was neglected in my bulb replacing furor. Gawd....I hope that bulb and ground will do it...I'll check it out! I did check the ground on the passenger side awhile back, because somebody mentioned something about a stop light ground causing cruise control failure.

So now it's hunt & peck.....hate the challenge of electrical gremlins.:(

Kevin
 

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89 300E; 00 E320
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2,515 Posts
check all standard fuses
exterior lamp failure monitoring unit-N7
high beams, low beams, fog lamps, standing/parking lamps
stop lamps, backup lamps, center high mounted stop lamp,
tail/parking lamps


exterior lamp switch, combination switch(low beam switch, headlamp flasher switch)
left and rightside marker lamp

stop lamp switch, starter lock out/ backup lamp switch
left and right license plate lamps

hazard flasher switch
combination relay (flasher)N10
turn signal switch
turn signal lamps (headlamps & taillamps)
turn signal indicators, audible turn signal solenoid (in instrument cluster)
 

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Premium Member
'92 300TE 4matic 280,000miles, '92 300TE 4Matic 'Ice Blue Metalic' 101,000miles
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10,388 Posts
Discussion Starter #11
"exterior lamp failure monitoring unit-N7"

Where would that particular item be...? Fuses have all been checked/replaced with newer style copper. I need to check the back-up lights though....forgot that one.

Kevin
 

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89 300E; 00 E320
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2,515 Posts
TE eh
W8 Ground, tailgate (cable connector) Left corner of tailgate, behind panel 241-5

& tailgate closing assist A12

A12 Tailgate closing assist Center of tailgate, behind panel 243-5
A12s1 Tailgate closing assist switch part of A12
 

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89 300E; 00 E320
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2,515 Posts
"exterior lamp failure monitoring unit-N7"

Where would that particular item be...? Fuses have all been checked/replaced with newer style copper. I need to check the back-up lights though....forgot that one.

Kevin
N7 Exterior lamp failure monitoring unit Rear of fuse box, position K

F1 Fuse and relay box Left side of component compartment 231-4

Fuse/Relay Box 102
 

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Premium Member
'92 300TE 4matic 280,000miles, '92 300TE 4Matic 'Ice Blue Metalic' 101,000miles
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10,388 Posts
Discussion Starter #14
Thanks for the info/diagrams...but I'm going to try some other things before I pop the tailgate panel off.

Kevin
 

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Premium Member
'92 300TE 4matic 280,000miles, '92 300TE 4Matic 'Ice Blue Metalic' 101,000miles
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10,388 Posts
Discussion Starter #15
<bump> and update:
I checked and replaced every single exterior light bulb I could find, including the license plate lamps. I was encouraged momentarily because the exterior bulb indicator went out after I removed the license plate lights and headed to the auto store. En route it came back on, of course.

I have to order a tie rod to finish my front-end work, so I'll include the fusebox relay I guess. I haven't replaced the headlights though.....maybe I should freshen them up and see what happens....well, there's the fog lamps as well.:rolleyes:

Kevin
 

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1993 MB 500E, 1965 MB 220b
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77 Posts
Exterior Bulb Failure

Kevin, Try to recall what driving activity you perform when the failure indicator actuates (same activity or various activities?). If my memory recalls, the indicator triggers when a bulb which should be actuating can not (for instance you step on the brake but a brake light is burned out, or you turn on the clearance lights but one is burned out).

If you happen to have someone driving with you next time it happens (and safety considerations allow) pull over & while you monitor the bulb failure indicator light, have them run around the car looking for the light which should be on but is not. BTW, did you check/replace the 3rd brake light (often overlooked)?

If you are still physically unable to see what light is not "on" while the faillure indicator is on, then it appears you'll have to dig in to the activities cbc atl suggests.
 

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Premium Member
'92 300TE 4matic 280,000miles, '92 300TE 4Matic 'Ice Blue Metalic' 101,000miles
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10,388 Posts
Discussion Starter #17
Kevin, Try to recall what driving activity you perform when the failure indicator actuates (same activity or various activities?). If my memory recalls, the indicator triggers when a bulb which should be actuating can not (for instance you step on the brake but a brake light is burned out, or you turn on the clearance lights but one is burned out).

If you happen to have someone driving with you next time it happens (and safety considerations allow) pull over & while you monitor the bulb failure indicator light, have them run around the car looking for the light which should be on but is not. BTW, did you check/replace the 3rd brake light (often overlooked)?

If you are still physically unable to see what light is not "on" while the faillure indicator is on, then it appears you'll have to dig in to the activities cbc atl suggests.
Define what the "third brake light" is, please? I replaced every bulb in the bulb strips, in the back, on both sides. Are you talking about that extra bulb on the driver's side back, that comes on when you pull the light control to it furthest position?

We've done all the checks here like that. I mess with the bulbs and start the car...the exterior bulb indicator is off. A few moments into the drive and it pops back on. I'm not even braking...just accelerating. It isn't much of a delay though before it pops back on.

This late with snow coming this weekend and still no pressure transducer showing up for my 4matic system, I'm not going into the interior panel of the rear hatch door.:eek: I don't mind buying a relay to test and then have as a back-up. Ordinarily though, I don't just substitute parts without pinpointing the problem.:thumbsup:
 

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Premium Member
'92 300TE 4matic 280,000miles, '92 300TE 4Matic 'Ice Blue Metalic' 101,000miles
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10,388 Posts
Discussion Starter #19
Located on rear window. Standard equipment for your MY. See photo.
Doh.....of course.:eek: I'm pretty sure it's working, but I didn't check it....thanks!

Kevin
 

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Premium Member
'92 300TE 4matic 280,000miles, '92 300TE 4Matic 'Ice Blue Metalic' 101,000miles
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Discussion Starter #20
Doh.....of course.:eek: I'm pretty sure it's working, but I didn't check it....thanks!

Kevin
Update: I'm about 99.99% sure the trouble is the 'third brake light'....which is out. Thanks DerFuror...:bowdown:

Anyway, like most things German 124 related, there is a 'process' for taking that plastic shroud off to get to the light bulb. I've pulled up, pulled down...off to the sides etc. I don't want to break the little gem so......search pulls up nothing so far, but I remember someone here telling all how to do it once....? I think they said to 'squeeze' the sides maybe and then up??

Kevin
 
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