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Discussion Starter #1 (Edited)
I blew a fuse while replacing the light bulb for the feet area lamp. I couldnt find any blown fuses in the front or rear fuse boxes...

now there is no lights or buzzer when I open a door.

so there must be an aux. fuse somewhere protecting this circuit...

anyone knows where is it?
 

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Discussion Starter #3 (Edited)
as I said, there are no blown fuses in either of the boxes...

also, I just noticed that the lights are not turning on when the driver door is opened (the side where the short happened), the passenger door triggering (opening) is turning all of the bulbs as it suppose to...

there is either separate fuses for the left/right sides triggers, or I messed up the light delay control unit...

I am digging into the STAR manual and WIS to see if there is anything about it...
 

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2003 Mercedes SL, 1964 Corvette StingRay Sport Coupe, 1992 Mercedes 300 SL, Porsche 911 Twin Turbo
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I replaced a light bulb for the map light(up with the mirror)and it is 5 watts bulbs.
Replaced the map light bulbs using regular 4 watt bulbs.

The result was that i just had a little glow in some of the bulbs and all of the warning lights on the instrument panel started to flash like a christmas tree.

The map lights is halogen lights so that is the reason why my car acted like it did because i used the wrong bulbs.

After i changed back to 5 watts halogen bulbs everything was okay again.
This might just be the map lights i dont remember the ones in the doors.

Check that you have replaced the bulb with the correct one
 

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Discussion Starter #5
I was actually replacing the light lens, and not the bulb, so the original bulb is still there and working...

I managed to contact the 2 leads together in the process, and that threw an over current protection somewhere, in the possible form of fuse, other than in the fuse box...
 

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'97 SL500, 06 Subaru Outback, LL Bean 3.0
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as I said, there are no blown fuses in either of the boxes...

also, I just noticed that the lights are not turning on when the driver door is opened (the side where the short happened), the passenger door triggering (opening) is turning all of the bulbs as it suppose to...

there is either separate fuses for the left/right sides triggers, or I messed up the light delay control unit...

I am digging into the STAR manual and WIS to see if there is anything about it...
I followed a thread with that exact same problem within the last month or 2 but can't find it. The poster just had that problem but no knowledge as to what caused it (might've been a car he'd just bought).
Seemed like it had to be the left door switch, but I can't remember how it turned out. The light delay control unit was never mentioned, though.
 

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Discussion Starter #7
I followed a thread with that exact same problem within the last month or 2 but can't find it. The poster just had that problem but no knowledge as to what caused it (might've been a car he'd just bought).
Seemed like it had to be the left door switch, but I can't remember how it turned out. The light delay control unit was never mentioned, though.
I found the post you re talking about... I also found a couple other posts made over the years about the same issue... no one posted a confirmed soluion either...

looking at the schematic, the thing is as confusing as heck, even for an EE (myself) :(




I am getting very tempted to get the N2/4 module out and see if it shows any damage or burned up PCB... since the fuses beyond that module are all intact...
 

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Discussion Starter #8 (Edited)
for anyone interested in following the schematic, the bulbs in the foot area are E17/1 and E17/2 and the 2 door switches are S17/3 and S17/4

furthermore, E15 is the headliner light, A1 is the gauge cluster, K24 is a relay, S21/8 and S21/9 are the windows lowering sensors,
 

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I found the post you re talking about... I also found a couple other posts made over the years about the same issue... no one posted a confirmed soluion either...

I am getting very tempted to get the N2/4 module out and see if it shows any damage or burned up PCB... since the fuses beyond that module are all intact...
I finally found it too.

http://www.benzworld.org/forums/r129-sl-class/1548321-seat-adjustment-6.html

I think the conclusion was the left door switch wasn't getting any power with the right door closed and he was gonna trace what should have been the hot wire back.

Maybe PM to jmerc6 and ask if he fixed it.
 

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Discussion Starter #10
according to the schematic, there should be no power in the door switch... the circuit is ground driven... meaning that the switch closes and provides ground to the N2/4 and the bulbs when the door is open... and cut the circuit open when the door in closed...

aka the switch leads never see positive current, instead, they have 2 states: ground / float

I dont know though, I need to grab my handy dandy fluke meter and confirm...
 

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according to the schematic, there should be no power in the door switch... the circuit is ground driven... meaning that the switch closes and provides ground to the N2/4 and the bulbs when the door is open... and cut the circuit open when the door in closed...

aka the switch leads never see positive current, instead, they have 2 states: ground / float

I dont know though, I need to grab my handy dandy fluke meter and confirm...

I don't see how that could work. It seems that everything should be grounded locally to the body or there'd have to be a couple extra miles of wires.
Mr. jmerc6 had power on the right side switch that worked.
Btw, does your driver's seat adjustment work with the left door open?

I THINK that I THOUGHT on the other thread that there would be a float or a neutral wire, MAYBE that got power from the right side sometimes.
 

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Discussion Starter #12
I don't see how that could work. It seems that everything should be grounded locally to the body or there'd have to be a couple extra miles of wires.
Mr. jmerc6 had power on the right side switch that worked.
Btw, does your driver's seat adjustment work with the left door open?

I THINK that I THOUGHT on the other thread that there would be a float or a neutral wire, MAYBE that got power from the right side sometimes.
That's how the fuel injectors in almost any car are wired... permenantly connected to the positive, and the transistor driven controller floats or grounds the other lead...

the reason being safety and durability, creating a semiconductor controlling the ground lead minimizes its chance of damage due to shorts in a negatively energized chassis (such as a car) by 66%, compated to driving the positive in a negative chassis...

and yes, you re right, it may seem inefficient at a glance, in terms of copper wires, but wires are much less expensive thant semiconductor...
 

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That's how the fuel injectors in almost any car are wired... permenantly connected to the positive, and the transistor driven controller floats or grounds the other lead...

the reason being safety and durability, creating a semiconductor controlling the ground lead minimizes its chance of damage due to shorts in a negatively energized chassis (such as a car) by 66%, compated to driving the positive in a negative chassis...

and yes, you re right, it may seem inefficient at a glance, in terms of copper wires, but wires are much less expensive thant semiconductor...
I'm sure you are correct re. the injectors where it's all built into the unit and there'd be no need for a seperate ground wire, but I can't see that lights, etc. would be rigged that way. The external lights and any others with "normal-type" bulbs obviously aren't, and the little all-glass Christmas tree bulbs with the 2 wires seem to have one permanently grounded.

And as I understood it, Mr. jmerc had power on the right side switch when that door was open and on the left side switch only when the right door was open.
.
? Do your driver's side seat adjustments work with only the left door open and no key??
 

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Discussion Starter #14
Do your driver's side seat adjustments work with only the left door open and no key??
No...

openning the door should do 3 things:

-turn the door lights on, and keep them on as long as the door is open
-enable the seat control function, as long as the door is open.
- turn the headliner lights on and keep them on 30 seconds after the door is closed, or until the car is started, or central lock is locked.


in my case, none of these things is happening, and all of these are driven by one switch... once the problem with the controlling circuit is located, all 3 will be resolved at once...

all of these functions were okay before the short happened, and they continue to operate normally for the passneger door...
 

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No...

openning the door should do 3 things:

-turn the door lights on, and keep them on as long as the door is open
-enable the seat control function, as long as the door is open.
- turn the headliner lights on and keep them on 30 seconds after the door is closed, or until the car is started, or central lock is locked.


in my case, none of these things is happening, and all of these are driven by one switch... once the problem with the controlling circuit is located, all 3 will be resolved at once...

all of these functions were okay before the short happened, and they continue to operate normally for the passneger door...
Thanks from all of your many friends and admirers for the post.
This is exactly how far Mr. jmerc6 got. He was gonna trace back what he thought should be a hot wire to the driver's door switch and wondered how to get under the carpet (driver's side, I think) to get to a connector lurking there. Then he disappeared, probably into the Great Abyss. Don't let this happen to you.
Please let us know how this turns out!

P.S. Fwiw, the wire from the passenger door switch activates some of the same things as the driver's door switch does, so wires from both switches would be connected together at these components. So opening the passenger door should affect voltage readings on the wires to (or from) the driver's door switch.

P.S. To make sure how they work, why not check the voltage on the 2 wires on the right door switch when the button is out (door open) and pushed in (door closed). The left one has 3 wires, but 2 should behave the same way.
 

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Bayhas, did you CK for voltage drop?

You can have power but maybe a loose connector/wire, bad relay, has voltage drop.
Or not enough voltage to operate the systems relays, etc.

Also you must CK the grounds.
Isn't the alarm also hooked on the same system?
As you know electrical work on a MB is a Royal pain....

After all it all started from an unintentional short.
From what I know the wire is coming from the right passenger door jam connector.

Regards,
aam.
 

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Discussion Starter #17
Alright! problem solved...

as I expected looking at the diagram, N2/4 is the offending component... MB p/n 012 545 68 32.

it is a small box behind the dashboard, you can access it by removing the passenger airbag or glove box, depending of what is installed in your 129.

easiest route is to replace it, but being an EE myself, I cracked it open and fixed it...

one of the connections on the PCB is too thin to take the short current, so it burned up and opened the circuit for the driver side...

few minutes of EE magic with the soldering iron, and the module is good as new... plug it back and... and we are back in business...
 

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I'm aware of the N2/4 you are referring to and in fact replaced mine, but it didn't help. I have gotten back to tracing the problem. My wife's 300CE tranny reverse is going to south, sooooo, I've started on it this afternoon.
My next step on the SL is to pull the carpet from the driver's side and check the connector.
 

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Discussion Starter #19
Yeah, that would be X18 connector in there...

I would say expose both, the N2/4 and X18, and using the diagram in this post, make sure you are getting appropiate triggering when the door switched are operated, you should get Ground/float.. the door switch will NEVER see positive +12V

the door switches are connected to permenant ground on one side, and to the control module on the other end. the module turns everything on that needs to be on (buzzer, lights, seat control switch) when it recieves the ground from the switch... the wire floats for the rest of time (connects to nothing)

also, if you tried a used N2/4, i would say it doesnt hurt to open it and look inside, from the way that box its made, and being unfused, my expert opinion is that box can get messed up if you look at it the wrong way...
 

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Thanks for the info. I'll take a look inside the N2/4 before I take the carpet out. I discovered the other day that if you are sitting inside the car and manually lock and unlock the doors the headliner lights are triggered. Does that give anyone another piece of the puzzle?
 
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