Xenon HID Ballast control unit
Xenon module fits all cars with D1S or D1R headlights and 35W Gas Discharge bulbs.
Control unit is responsible for powering up HID bulbs and controlling them, when turn on or off.
If your xenon lights have started to blink, shutting down for no reason or don't work at all and you did check HID bulbs, it means that  xenon ballast needs to be replaced.
When replaced Mercedes-Benz A2129007804 xenon control unit, it will need one-time coding.

The most common warning messages for mercedes-benz
Low beam left
Low beam right
Dipped beam left
Dipped beam right
Active Light System currently unavailable
Left dipped beam
Right dipped beam

This is an after-sales replacement part, not an original genuine product, and is used to replace the following part numbers:
A2128205626
A2129024202
5DC 009 060-20AN
5DC009060-20AN
A2129007804
212900780480
5DC009060-20AL
A2129003502
A2128205626
A2129086701
5DC009060-20AK
A2129001200
A2128205626
A2129023101 A2129023100
5DC009060-20AM
A2129007804
A2128205626
A2129024202
A2128205526
MA212900780480
5DC009060-21

Compatibility list:
for Mercedes-Benz E Class W212 Saloon Sedan Pre-Facelift 2009 2010 2011 2012 2013
for Mercedes-Benz E Class S212 Estate Wagon Pre-Facelift 2009 2010 2011 2012 2013
for Mercedes-Benz E Class C207 Coupe Pre-Facelift 2009 2010 2011 2012 2013
for Mercedes-Benz E Class A207 Convertible Cabriolet Pre-Facelift 2010 2011 2012 2013
for Mercedes-Benz E200 E250 E300 E350 E500 4MATIC BlueEfficiency Petrol Gasoline
for Mercedes-Benz E63 AMG 4MATIC
for Mercedes-Benz AMG Line
E200 E220 E250 E300 E350 BlueTEC CDI 4MATIC Diesel
Please note: This list is not full, it may fit other car models as well, please check provided part numbers, pictures and compare to your old parts.

Package Included: 
1 x Xenon Headlight Ballast Control Unit(As the picture shown)
1 x D1S Bulbs