Just a dumb guess - maybe the PO (previous owner) forgot to remove all the wiring from the aftermarket kit?

 

I am not an expert, but the other guys might chip in on this thought.

Perhaps original owner did not buy error free LEDs and used a balance resistor of some kind?

Just thinking out loud.

@efair
@curro101
@Sneaky Pete

i cant find any rewiring or adapters.

 

I looked at the wiring diagram for A USA R171 tail light, left side, it is confusing to me (so I probably will just confuse you - sorry). It shows the wire assignments as:


1) Brown - ground
2) Black/White (turn signal)

3) Green/White (fog lamp - LED)

4) Black/Red (side marker lamp - I am not sure what this means)

5) Grey/Black (stop lamp/tail lamp/parking lamp - LED)

6) Grey/Yellow (backup lamp)



Your picture shows the correct wire colors, but your large plastic connector looks like a wiring adapter attached (at the bottom of your picture). Can this adapter be removed? Mine does not seem to have this large plastic connector.

 

the white?
this holds the lamps /bulbs

 

I am not an expert, but the other guys might chip in on this thought.

Perhaps original owner did not buy error free LEDs and used a balance resistor of some kind?

Just thinking out loud.
@efair
@curro101
@Sneaky Pete

 

Like I say, not an expert.

Worth having a look at the wiring harness that is routed by the boot hinge.

It can wear and fray.
Mike wrote a good explanation.
Follow the link in the quote below for some detailed pics too.

We'll that was a cold day spent outside .. but pleased with the results.

First I found an old repair that had failed as they left the joint at the bend point of the wire!
So I then cut the old wiring back and made new joints protected with heat-shrink and new protective cover, pushing the joined wires up into the inside of the boot and then repeated half way down the lower strut (so the joint is protected by the plastic wire cover / protector).

I used a 7 core 'tow bar' cable plus a separate brown wire as that's twice the size of the others. also managed to feed the cable for the reversing camera through the protector at the same time so very happy with the repair :smile:

from
https://www.slkworld.com/general-di...m/general-discussion/255514-what-did-you-do-your-slk-today-336.html#post4470463

 

In your first picture - the black square - is that one piece? Or will it separate into two pieces?

 

black square?
this is the connector from car electric zu the rear lights.

 

Yes - but is it two pieces that can come apart?

 

Sure

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What happens if you plug the top portion directly into the factory tail lamp?

 

This is the factory connector of the lamp.

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All looks OK as far as I can tell from those pictures. Pin#4 on the tails is for the side-marker which is a small parking lamp that is only there on USA-spec cars. You can see from the pictures that the wire for this pin is missing, as is normal for ROW-spec. I don't see any aftermarket stuff in that picture.



Is it possible that there's something spliced into the car wiring further up the wire harness in the direction of the SAM?


Usually that message means that one of the important bulbs is out and the car has re-routed that function to a different light I think. The SLK is really good at making sure you have some kind of tail light illumination even when multiple bulbs burn out (like it will use the fog or backup lights instead of the normal LED strip if the SAM decides that the strip is not working).

 

@Burnsi - apologies for my non-help. My tail lamps are different from yours - the white part of yours is black on mine, I didn't recognize what I was looking at.


Attached is a picture of the Rear SAM wiring in this area.

 

In this wiring Diagram the fog lights are with led.
In my case the fog lights are bulbs.

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In this wiring Diagram the fog lights are with led.
In my case the fog lights are bulbs.

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The stock fog lights on the R171 are definitely incandescent, not LED. That wiring diagram seems incorrect to me. I've been hunting all over my hard drive to find old captures I did of this part of the wiring diagram back in 2012 when I was doing modifications for after market tail lights, but all I could find was pictures I already edited to reflect the after market situation, not stock... I'll take a look at my service CD tonight to see what the wiring diagrams look like according to that thing.


From what you're describing in your original post, it sounds like the light units are working correctly, and it is the wiring from the SAM to the housings that is having an issue. Is the message coming on for both left and right-hand side of the car, or just one side? If it is just on one side, you could take the lights out and swap them between left and right (you can't mount them like that of course, but just put the housings in the trunk and wire them up that way). Actually I'm not sure how easy that will be because usually the wiring harnesses are exactly the right length so you may not be able to reach the light if it was in the trunk... Anyways, worth a shot.

 

unfortunately its on both sides.

 

It wouldn't be the first time an MB diagram was wrong. I'm wondering if there is any relevant coding to help. I'm also somewhat perplexed how one circuit can control all three of stop, tail, and parking!

 

WIS shows the same error in the diagram. My guess is they inadvertently used a wrong symbol for the fog lights and the pin numbering is still correct. According to the manual only tail/brake lights are leds.
If your lights are off braking will light up all the leds. If you switch your lights on only half of the leds for the taillight will light. If you brake the other leds will come on. I guess that's how it works.
https://drive.google.com/open?id=1d4uMQ3uOJ7QXWeRXXJexm99vvHSYnaKx


Maybe the cause of your error is that the PO connected the aftermarket lighs according the symbol in the diagram? I would check the wiring and take the numbering in WIS or the pic as a guide.

 

Have you tried to pull up all the trunk carpet and look at the Rear SAM directly to see if there's any components spliced into any wires that look out of place?


See middle of page 1 of this thread for what Rear SAM looks like after carpet is removed and metal panel is loosened and rotated:


https://www.slkworld.com/slk-r171-g...171-general-discussion/535069-powering-central-locking-via-rear-sam-module.html


See here for instructions on pulling up the carpet:


https://www.slkworld.com/slk-r171-general-discussion/38233-fuse-box-trunk.html

 

@Sneaky Pete are you sure about your"half and half" theory? I'm not arguing with you, I'm just curious after reading some Google results. I went out to my car at lunch to see if I could confirm your theory... I had to use my phone to make a video and I got lots of funny looks! After doing so, I couldn't confirm or deny because the lens is impossible to see through.

 

@Sneaky Pete are you sure about your"half and half" theory? I'm not arguing with you, I'm just curious after reading some Google results. I went out to my car at lunch to see if I could confirm your theory... I had to use my phone to make a video and I got lots of funny looks! After doing so, I couldn't confirm or deny because the lens is impossible to see through.

It's actually not half-and-half, but PWM for tails, vs "always on" +12V for brake lights.



Here's an o-scope showing the duty cycle of the PWM signal that constitutes the tail light signal. It has a duty cycle of just 7% on vs 93% off. I was surprised how short the tails blip on to produce the normal rear light illumination:

 

So it's not separate LEDs? The tail and the brake use the same LEDs, just with a different signal applied?

I read somewhere that the lumen ratio is supposed to be 10 to 1 - the brakes should produce 10 times the lumens as the tail lights- so 7% is about right.

 

So it's not separate LEDs? The tail and the brake use the same LEDs, just with a different signal applied?

I read somewhere that the lumen ratio is supposed to be 10 to 1 - the brakes should produce 10 times the lumens as the tail lights- so 7% is about right.

Yeah that sounds about right then. It is indeed the same bank of LEDs just driven differently. I actually just finished a control circuit that takes this 3-state signal and drives 2 completely separate banks of LEDs (one for rear, one for brake) at full brightness:. This was to replace a part of the popular after-market tail lights for the R171 that had broken for a forum member here.



Sorry about derailing the thread. Back to your regularly scheduled programming!

 

Did you make these traces with the lights disconnected or connected?

 

Are you talking about that o-scope picture? That was with light attached. I think the car would have a cow if you turned the lights on without any housings connected. Probably some of what the O.P. is experiencing.

 

Burnsi, none of this is going to help you with your issue. I do wonder though, 1) how the SAM knows there is a short or an open in the LED circuit 2) if the SAM requires some type of reset to restore it to normal behavior, and 3) if the SAM keeps transmitting the PWM signal even after it detects the line is open.

I'm going to have a look at SDS tomorrow.

 

I was mesduring bolts on All lights.
All of them are working, only the gray/Black was not.
This is on both sides.

I deleted all error Codes and cut the battery for 10 min.

Same errors.
Maybe i have to pay some new lights for testing.

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The SAM should not have to be reset to "see" the lights again after they were temporarily removed. I've done this many times and I've never had to do anything like that.

The rear/brake light will draw a maximum of 50mA. So at 12V this means you can splice a 220Ohm/1W resistor across across the #1 and #5 pins to make the car think that the light is there. You could do this on both sides simultaneously and at that point you should be able to remove the lights completely and still have the car think that they're there.

If it still ends up in "ersatz" mode, and there is *definitely* no modification to the wiring loom between the SAM and the tails, I would start to suspect the SAM itself being defective.

 

@Burnsi what was the voltage on the gray/black when you press the brake pedal? 0V?

 

Do German cars have the center stop lamp (CHMSL) too? I'm wondering if this might be in play.

 

We should not forget that his car is a German version and may be built to different Gm/EU regulations....maybe lights and/or wiring are not US standard? I would suggest going to the MB dealer in Germany and seeing what all the rear lights actually are for this specific car and if different from what is in the car. Another idea...could different front lights cause a weird issue also?

Baja-D

 

We should not forget that his car is a German version and may be built to different Gm/EU regulations....maybe lights and/or wiring are not US standard? I would suggest going to the MB dealer in Germany and seeing what all the rear lights actually are for this specific car and if different from what is in the car. Another idea...could different front lights cause a weird issue also?

I've worked on the R171 tail lights a *lot* , including supplying many modifications to European owners. See here:


https://www.slkworld.com/general-mo...m/general-modifications-r171/29482-do-led-taillights-cause-bulb-out-errors.html


The difference between North American and ROW (Rest Of World) spec is only the lack of pin#4 (side-marker) on the Euro tails; the rest is identical.



The headlights are on a completely separate SAM so they do not interact. The symptom he is seeing is typical for a burnt-out rear light on either side of the car: it goes into "emergency" mode and uses other bulbs in the tails to take over from the normal rear light bank.


I think the experiment with the resistor is worth while. Those are less than 1 Euro each which is quite a bit less than buying a second set of tail lights to experiment with. I'd say if the resistor experiment does not give any new information, it's time for a dealership visit (and a new SAM? hope not, but ...)

 

Hi,

I got xentry now and i can test the lights.
Left are OK, every Light works.
When i Switch the right Light or Brake Light on the Software Shows for a Quarter second on an goes to off.
My Voltmeter is to slow but i can messure that i got voltage on the right wire.

Next i've tried a used rear Light and i got the same errors. So its nö Problem with the headlights.

 

Burnsi,

I'm having same issue with fog lights but only on the right hand side. and the left side license plate lamp. I thought the fog was a connector issue as when I purchased the it was not working and I seem to recall getting it to work by wiggling it a bit. I ignored it b/c I rarely use the fog lights. Now I would like to get it working and it is irritating me. The license plate light went out, started working when I closed the hood then went out again.

I'll let you know if I work anything out.

 

...I'm having same issue with fog lights but only on the right hand side. and the left side license plate lamp. ...

Your fog problem is actually not a problem: the rear fogs on the R171 only come on, one side at a time. Normally the left fog is on when you pull the light switch all the way out. The right fog only comes on when the car detects a problem with the left one. There is a way to program the fogs to both come on simultaneously but from the factory this is not how it works.



The license plate light is a separate issue.