So my passenger side low beam headlight intermittently went out, then came back on, then finally went out over about a two week's period of time. I have the Bi Zenon HID headlights with the D2S bulbs. So I swapped bulbs and igniters, and determined (incorrectly) the fix must be the ballast. So I ordered a new ballast and installed, but the light was still out! So I finally determined it must be the connector. I've attached a picture of the low beam connector and, sure enough, it was corroded enough to cause the intermittent low beam headlamp. I wanted to pass along my thoughts to hopefully help someone else who has a similar problem with their low beam HID headlamp.

So, if you have Bi Zenon HID Headlamps and your low beam is out, there are four likely items that could be the culprit:
1. The D2S bulb (easy to swap with the other good one to determine if it's the problem or not).
2. The igniter - the igniter is affixed to the back of the headlamp bulb and RARELY is the problem. Still, swapping with the good headlamp igniter is a good way to rule it out.
3. The ballast. The ballast is OFTEN the problem when a bi xenon hid low beam headlamp is out and the bulb is ruled out. There are various places to find the ballast. I opted for the more expensive FCP Euro option, because their parts are warranted for life.
4. The low beam connector on the back of the headlamp assembly. This turned out to be my problem.

I ended up removing the headlamp assembly from the car to initially get access to replace the ballast. To do so, I did the following:
1. Turned the front wheel outwards towards pax side. Removed the three plastic pin brackets to pull back the inner wheel lining. Removed the vertical pax side bracket that holds together the bumper cover and upper fender (T-15 or T-20 bit). Need to pull bumper cover forward about 3 inches.
2. Remove the two plastic pins at the front center of the engine that connect the upper part of the grille to the engine. This will help to pull bumper forward to allow room to remove headlamp assembly.
3. Remove three bolts that hold the headlamp into place. These are 10mm bolts. Two on top of headlamp and one on the side inside fender well. Once these three bolts are removed, you can pull outward on the bumper cover and then work the headlamp out from the front. I put a towel on the bottom portion of the bumper cover to protect from scratches as I pulled the headlamp assembly out.
4. I left the connectors intact and initially just positioned the headlamp vertically to gain access to the three T-20 torx screws holding the ballast into place. I replaced the ballast and the light was still out for me, so I proceeded to the connector. In hindsight, I should have gone to the connector before spending the money on the replacement ballast.
4. The low beam connector is immediately behind and lower than the low beam light assembly. It's a four wire connector, and tt's a push button to unlock the connector. Once you take the connector out, you can inspect for corrosion. If there is corrosion I used some CRC Electronic Cleaner from AutoZone to clean the connector. It dries quickly, but I waited 10 mins to put back together.

The female portion of my connector was corroded and the corrosion in the connector resulted in the intermittent low beam light (picture attached). The CRC Electronic Cleaner and an old toothbrush removed most of the corrosion. I also observed that two of the four female connectors openings were loose (opening somehow got bigger), so I used a pick to pull close the female connectors a bit more so there would be a snug fit between the female connector and male portion of the headlamp. ​​​​​​Ideally, you could use a connector remover tool and properly "crimp" the connector to make it tighter, but the pick to make the connector tighter worked for me. I also used a $1.50 Connector Protector lube found at the checkout counter of AutoZone to protect the connection from future corrosion.

If your connector is good and you determine you need to replace the ballast, you can use a T-20 bit to remove the three screws of the ballast to replace. The ballast is located on the bottom of the headlamp assembly. Btw, if you call Mercedes to ask for the ballast part number, they will give you two part numbers. One for the ballast and one for (I think) the HID direction control. The ballast is the part that usually needs to be replaced. That part number is Mercedes 002 820 23 26. There are several revisions of this part number due to the age of the part, but you should be able to find a compatible part. The part FCP sent me had Hella part number 63126907488.

Reassembly is the reverse order. My low beam headlight is perfect now. Hope this helps anyone who has tried to replace bulb, igniter and/or ballast and the headlamp is still out. Sorry for the lack of pics, but I was just wanting to get my one eyed monster back to two eyes!

Cheers,
James

 

Just bumping this for more awareness for folks diagnosing headlight issues. This is a great reminder of an easy step to inspect before going to the trouble completely removing the headlamp assembly.