Recently, we've had lots of faulty light bulb messages on our 09 ML350. So I check the bulb, and sure enough, it's dead. Then, the message doesnt appear anymore, so I check again, and OH would you look at that! It's working fine. It's been constantly doing that and it was really bad with the brake lights, so we took it to MB of Seattle and they fixed some wiring or something. We just got a warning for a dead rear right brake light bulb, which was dead, and now it's not. I don't know what's going on but I don't really want to take it to MB before I get an idea of what's going on because they'll replace like 4 things before replacing the actual problem part and charge us for all parts. Thx in advance.

 

Do you have LED tail lamps?

 

Nope, just the good old incandescents.

 

Here is the procedure and the part number, x2, is located.

Follow the instructions and after the little flaps are open, you will need a thin needle to extract the appropriate wire.

Do not cut the wires to make things easy as it will compromise the system.

 

I'm slow, are these instructions on how to replace the wiring harness? If so, i should mention that I had this same problem with the front right side marker bulb. Would I also replace the harness there?

 

It is only for the rear.

 

On my 2009 ML550 with the same incandescent lights, the problem was slight corrosion on the contact between the bulb holder and the frame of the light assembly (which I assume caused intermittent grounding problems). I took the holder out, removed the bulb, then gently used sandpaper around the orifice, and around the part of the holder that contacts the frame, put it back in and the problem has not shown up since.

 

I'll try that out. If it doesn't work, I'll just have the MB dealership replace the harnesses. I think the front side marker doing this was a weird one-time thing, as I haven't had it since I first saw it. Here's a picture of what we've been dealing with lately, but sometimes the order of bulbs not working is reversed, etc...

 

I just finished sanding the bulb socket contacts and the part of the frame where they go (admittedly not that good, as I didn't remove the tail light assembly, I just did it from the right rear quarter panel) and I'm still getting the same results. However, it looks like the lower tail light bulb that illuminates on the right side when the brakes are pressed isn't supposed to illuminate on the left side when the brakes are pressed, but rather when the rear fog lamp is turned on. So, in this case, the message on the dashboard that we've been getting (Rear Right Tail Lamp Out) makes more sense, as the only bulb that's not illuminating when it's supposed to is the upper right brake light bulb. So, I replaced that light bulb. Didn't work. I swapped the left brake light bulb socket and bulb with the one on the right. The left brake light still works and the right one doesn't. This makes me think there's something wrong with either a harness or the contact on the frame, because as I said earlier, I didn't sand it very well. Here's a video of the issue. First, I turn the parking lights on. Then, I turn the parking lights off and turn the car on. I test the brake lights a few times. I turn the parking lights back on and test the brake lights with those on. Then I turn on the rear fog lamp while the parking lights are still on and test the brake lights.
https://drive.google.com/file/d/0Byv...ew?usp=sharing
What should I do to remedy this? I should add, I'm looking to replace the current assemblies with Anzo LED assemblies in the future, so keep that in mind when giving me suggestions on what to do. Thanks in advance...

 

I don't know if anyone has anything to add, but we got a quick and random message that the left rear brake light bulb was out. However, that message is gone now and the left rear brake light is working fine. We're gonna take it into Mercedes, and I'm thinking of having them replace the brake light switch, brake light relay(s) and all harnesses going to the brake lights. Should I add anything? And does anyone know how much it'll cost?

 

There is no brake light switch as there used to be nor is there a relay as there used to be.

I provided you with the fix but you completely ignored it.

 

Sorry, I've been working with a 1991 Land Cruiser for a long time now, which has all that crap. Haven't much experience with the odds and ends of the electrics of new cars. I didn't completely ignore you. I'm just definitely not up to doing all that work myself. You also didn't specify that that would definitely fix the problem. So shall I go to the service shop and have them replace the harnesses?

 

Automotive forums are for self-help information and procedures, not for telling you to go to the dealer.

As for not telling you it would definitely fix the problem, I posted a technical bulletin from Mercedes addressing your problem directly. If you would have asked that question 10 days ago, my answer would have been YES.

Good luck at the dealer. They are going to sell you something else which will stagger you.

 

Sorry about that. And I can use the forum however I want. I wanted to use it this time to just diagnose my problem. There's no way in hell I'm touching any wiring in a Mercedes. I don't have the confidence and like I said, I'm used to working on an easy 1991 Land Cruiser. I'll take it to an independent servicer near me, and I'll tell them to replace the harness and nothing else. Thanks again for your help.

 

You were just told there is a Service Bulletin for this that simplifies the repair. That you don't want to do it because you don't feel comfortable doing the work is fine, but then saying you'll take it to the shop to blow a pisspotful more money instead of asking them to do what the bulletin says? That's just stupid. You should have just said you wanted the most expensive solution in the first place, and saved everyone the trouble of trying to help you fix the problem reasonably without having to blow a large wad of cash.

 

Thank-you.