W124 weird console light behavior ... - PeachParts Mercedes-Benz Forum

BodhiBenz1987 · #1 12-12-2006, 02:25 PM

Starting last night I noticed this behavior:
All of the lights on the console and cc panel work just fine when the headlamps are switched on. Last night I turned the headlights off as I was pulling into a spot. My foot remained depressing the brake as I did so, and I noticed that some of the backlights on the console and center panel started flickering rapidly. The button for the rear dome light, the headrest-drop button and another button between them (can't remember which) flicker, and all the lights on the shifter and behind the window controls flicker ... just fluttering on and off. When I release the brake, they all go dark, as they should be. When I turn the headlamp switch on (brakes depressed or not), all the lights come on, as they should. What's the connection between the brake and the center lights? Is there a ground somewhere that's failing? I understand little about electrical function, so I'm having a hard time hypthesizing as to what may be going on. Again, everything is normal when I'm not pressing the brake pedal down. Lights work perfectly when the switch is on. Only bad combination is lights off + brake depressed.

justinperkins · #2 12-12-2006, 02:40 PM

My first thought would be the brake pedal mechanism literally tugging/pulling on the interior lighting wiring, which comes from the headlight switch.

Seems like a long shot, but more likely than there being an electrical relationship between the brake pedal and the console lights.

Are you sure it was only the interior lights that were being funny or was it even your exterior lights?

BodhiBenz1987 · #3 12-13-2006, 12:32 PM

Quote:

Originally Posted by justinperkins

Are you sure it was only the interior lights that were being funny or was it even your exterior lights?

Yep, headlights don't do a thing when turned off, brake or no brake.

Any ideas, guys?

I feel like I'm in a rave club when I go to park the car.

Jeremy5848 · #4 12-13-2006, 12:41 PM

Sounds like something electronic is getting a partial ground (or power) through the brake light switch. I'm a new 124 owner (3 weeks!) and don't have a manual yet so all I can suggest is to check all of the fuses and connections, make sure they are clean and tight. I'll be able to guess more accurately after I see a schematic.

BodhiBenz1987 · #5 12-13-2006, 02:34 PM

Quote:

Originally Posted by Jeremy5848

Sounds like something electronic is getting a partial ground (or power) through the brake light switch. I'm a new 124 owner (3 weeks!) and don't have a manual yet so all I can suggest is to check all of the fuses and connections, make sure they are clean and tight. I'll be able to guess more accurately after I see a schematic.

Thanks. I have the manual but when I look at the electrical diagrams, I feel like I'm looking at ancient code language. I know darn well that I have the capacity to understand all of it ... it's just something I never learned. Now that I have the interest, I've asked for all sorts of textbooks for Christmas ... but it's gonna take me a while to learn. For now, I can't make heads or tails of the diagrams. But I'll study them a little more.

thornton · #6 12-13-2006, 02:38 PM

I had the exact same situation on my w124. Totally unpredictable as it would happen for awhile, and then not, and then back again.

At the same time I would occasionally blow a fuse from the brake lights.

Finally found that I had a small bit of sheathing that came off one of the wires in the rear tail lamp assembly.

New assembly and no problem since.

Good luck

BodhiBenz1987 · #7 12-13-2006, 03:51 PM

Quote:

Originally Posted by thornton

Finally found that I had a small bit of sheathing that came off one of the wires in the rear tail lamp assembly.

I'll check this ... I did have one of the tail lamps out recently to do some rust repair around it. So maybe I tugged something when I was removing or installing it.

justinperkins · #8 12-13-2006, 04:21 PM

Quote:

Originally Posted by thornton

I had the exact same situation on my w124. Totally unpredictable as it would happen for awhile, and then not, and then back again.

At the same time I would occasionally blow a fuse from the brake lights.

Finally found that I had a small bit of sheathing that came off one of the wires in the rear tail lamp assembly.

New assembly and no problem since.

Good luck

I could see this causing a blown fuse, but flicker the dash lights?? Is the W124 E-Class really that crazy? I hope not.

pmckechnie · #9 12-13-2006, 07:35 PM

The only connection between the brake lights and the console lights is the tail/brake light assemblies. If a bulb looses its ground, brake light power will feed back through the tail light wireing to the dash lights. Follow along and I will try to explain how I find problems like this.
First, turn on the parking lights and look carefully at both sides of the car and make sure both sides are the same. Look for the brightness of the lights on each side. They should be the same or close to it. Now with the parking lights still on, have someone press and hold the brake peddle. The brake lights should come on and be brighter than the parking lights. Again, make sure both sides are the same in brightness. Next turn on the emergency lights. Now the parking lights, brake lights and flashers should be going. Again check both sides. My guess is that in one of the above things you will see a difference. Just investigate this difference and you will find your problem. The same proceedure works on the front if you have something strang going on there. I do this first for all lighting problems and 90% of the time it will get me started in the right direction.
By the way, I've been doing this for probably 50 years.

justinperkins · #10 12-13-2006, 07:39 PM

Quote:

Originally Posted by pmckechnie

The only connection between the brake lights and the console lights is the tail/brake light assemblies. If a bulb looses its ground, brake light power will feed back through the tail light wireing to the dash lights. Follow along and I will try to explain how I find problems like this.
First, turn on the parking lights and look carefully at both sides of the car and make sure both sides are the same. Look for the brightness of the lights on each side. They should be the same or close to it. Now with the parking lights still on, have someone press and hold the brake peddle. The brake lights should come on and be brighter than the parking lights. Again, make sure both sides are the same in brightness. Next turn on the emergency lights. Now the parking lights, brake lights and flashers should be going. Again check both sides. My guess is that in one of the above things you will see a difference. Just investigate this difference and you will find your problem. The same proceedure works on the front if you have something strang going on there. I do this first for all lighting problems and 90% of the time it will get me started in the right direction.
By the way, I've been doing this for probably 50 years.

That's awesome that you figured all that out. It almost makes me wish I had light problems so I could solve them in a snap with this awesome technique. Almost.

BodhiBenz1987 · #11 02-25-2007, 08:40 PM

FIXED!!!

Yeah, I know ... it's two months after-the-fact ... but I had to put it on the back burner because of weather and all that junk. This week I broke out the wiring diagrams and learned about circuits (it's been since sixth grade, so I gave myself a "refresher course"). Turns out all the lights that flickered with the brake pedal depressed are part of the 58d circuit (the lights not on that circuit stayed unlit, as they should have), which seems to connect to ... the taillight harnass connection, which, obviously, connects to the taillights. So, like you guys said, it made sense that a ground was off on one of the lights. I didn't get a chance to use your technique pmckechnie, since I had no one to help me push the brakes while I looked. I just went back and checked the grounds, both looked OK, but then checked connections ... the lefthand connection was loose on one end and had a cobweb (gasp!) kind of stuck between it and the plug. I cleaned it off and securely connected it. Since then ... no flickering! Obviously the connection was on well enough that the rear lamps were functioning, but maybe the circuit couldn't get to the ground wire. I had replaced that lamp lens cover right before the problem started, and my guess would be I jerked that connection around and boogered it up when I was doing that.

But, all seems well now. Cool.

If nothing else, I had a lot of quality time with wiring diagrams over this past week, and now I see them whenever I close my eyes.

optimizer · #12 11-23-2012, 05:44 PM

I'm having this same problem, but I checked all the grounds for the 3 brake lights and they all seem fine - clean and good connections.

Is there somewhere else I should be checking the grounds?

Codifex Maximus · #13 11-25-2012, 01:14 AM

Quote:

Originally Posted by BodhiBenz1987

Yep, headlights don't do a thing when turned off, brake or no brake.

Any ideas, guys?

I feel like I'm in a rave club when I go to park the car.

I know when the blinker assembly starts to go, sometimes it will flash rapidly. You may have feedback through that circuit due to a possible short. Test it by turning on your flashers and then trying what causes the issue. See if there is any different result.

BodhiBenz1987 · #14 11-25-2012, 05:23 PM

Quote:

Originally Posted by optimizer

I'm having this same problem, but I checked all the grounds for the 3 brake lights and they all seem fine - clean and good connections.

Is there somewhere else I should be checking the grounds?

Actually now that I go back and read this over, I wonder if this problem was related to this one that resurfaced this year (the part about the interior lighting, fixed by rewiring the rear door window switch): W124 electrical fun: Two problems. I'm not sure how the brakes tie into it, but if you have a short in the wiring that runs to the rear door, it could cause some odd behavior. It's the same circuit as all the lights that were (in my case) flickering. I kind of forgot about this problem ... when it resurfaced this year, they were simply out, unrelated to the brakes.