If you want to change your H7 Halogen bulbs for H7 LED bulbs in your C207 W207 E350 E550 Coupe.
you need to get some H7 LEDs and then you need to get some adapter clip things like this. I just searched Mercedes H7 Adapter or Mercedes H7 Clips or something into ebay.



Now the H7 LEDs will fit into your headlights. The problem is that the twist on cover that seals the headlight hits the heatsink for the LED bulbs and you can't close the headlight back up.

Now, if you got low profile LEDs that have a short heatsink at the bottom/back, you will probably get errors of the light turning off and on constantly because they are not high enough wattage/voltage draw. I know this because I got this with two different sets of those.

You don't want to be a dumbass and get dust and dirt inside the headlights, so, you need to replace the twist on headlight cover with one that accommodates the LED bulb heatsink.

This is what the original is like


It is 1305219121 or 15822200 or y1260y y1232y

My car is a 2010. I don't know if there is a facelift, and if there is, if it is different, but if you pull the rear headlight covers, you can look for your current part number on the low beam cover.

As you can see, this cap is flat, and it hits the bulb, and you can't close the headlight to seal it from dust and dirt and maybe even water.

So, you need a cap that has more depth.
Here are pictures from the ebay listing that I purchased from
A possible part number is y1035j





The one I received, I think it looks like the last picture, but I assume the deeper cap as depicted in the earlier photos should work great too
Maybe this is the ebay listing I found. Who knows if that link is still good by the time you are reading this. Check the part numbers from and pictures from above though to see what you can find.
Hope this helps.

 

Sadly, in the UK if a vehicle was first used on or after 01 April 1986 then the conversion will fail the MOT (annual vehicle test). Prior to the date a vehicle cannot be failed merely on the conversion unless they fail other requirements. Seems wrong should a vehicle used after 01/April 1986 and be converted and fulfill beam pattern etc requirements and have improved lighting be failed.

Class 3,4,5 and 7 vehicles

For class 3,4,5 and 7 vehicles, the defect ‘Light source and lamp not compatible’ only applies to vehicles first used on or after 1 April 1986.

Should a vehicle be presented for an MOT test with conversions before 1 April 1986 they must not be failed with immediate effect.

Vehicles presented with converted halogen headlamp units first used on or after 1 April 1986 will continue to be failed.

Headlamps must comply with all other requirements of the test and headlamp aim.

The cars and passenger vehicles inspection manual will be updated shortly.