Driver side Low beam headlight.
Began flickering 8/2017.
Replaced ballast. Worked fine.
Stopped working completely 10/17.
Replaced ballast 2/9/18. Worked fine.
Stopped working today, 2/19/18.
Both replacement ballasts were purchased from "eBay - rsocal45". Not implying this supplier is the issue - only that I did not purchase the replacement ballasts directly from Mercedes.
Any suggestions greatly appreciated.

 

Return it since he seems to offer a warranty.

 

Thanks.
I am actually wondering if the problem is not the ballast but rather something causing the ballasts to fail.

 

If you are confident in the quality of the lighting components, i'd have to say either you driver or passenger side SAM is bad..... Pretty easy fix but annoying af.

 

By SAM do you mean the entire fuse block. I googled it by did not find a driver side and passenger side SAM. Please explain.
Also, where would the SAM's you are referring to be located?

 

Front SAM N10/1 -> E1n4 supply module -> E1n2 ignition module -> E1e2 left low beam. See attachments to understand system.

 

Thank You!
The headlight assembly I have is made differently. There is only one module that plugs in to the bottom of the headlight assembly.
See photo.
The one with the yellow label was in the vehicle when I purchased it. Low beam drivers side failed in Aug 2017. I replaced it with the one with the white label. Light failed again in October 2017. I replaced it with another one that is still in the vehicle.
I assume the diagrams you sent would still be similar to my vehicle.
Is the N10/1 SAM something I can unplug and switch with the N10/11 SAM?
Thanks for your patience.

 

The white label has a W212 part number. Unless the control units for xenon's superseded part numbers I'd be concerned as to why it doesn't have a W211 pn, the one with the white label.

 

Here are the correct (compatible) part #s.

 

Thank you so much!
I really appreciate your help.
Going to try and find ballast A 211 870 90 26.

 

Thanks for the help everyone!
I replaced the ballast again with A211 870 55 85 (the OEM ballast calls for A211 870 90 26).
Closest thing I could find.
Checked the passenger side ballast while I had the car apart. It is same A211 870 55 85 part number. Probably was replaced at some point but has been working for the 3 years I have owned the car.
Hoping the problem is solved. Skeptical because the last ballast (same part number) lasted 8 days.
Time will tell.
Point of reference: The replacement ballasts I have been purchasing are $105 each. Only source I could find other than Mercedes dealer ($670 for the ballast and dealer would have to order it.)
If someone knows of a reliable, somewhat reasonably priced ballast source I would like to know for future reference if the problem returns.