I was searching for a full replacement of the headlight assembly with HID and Projector headlamps but I've given up - unless someone says not to!

To make it simpler, I'd like to replace the standard (halogen?) with brighter HID bulbs ... is there a conversion kit that will plug into the original Mercedes headlight assembly?

I realize it'll be more than just plugging in a bulb since it needs a ballast but what have others used who upgraded to HID lights??

 

There are "kits" sold online that include a rebased HID bulb that will fit into your halogen housings, but I wouldn't recommend them. Most of them don't place the arc in the proper position, which will drastically change your beam pattern. Even if the arc is in the proper position, the characteristics of a HID arc are very different from a halogen filament, resulting in less than optimal light distribution. The result of these kits is usually too much foreground light (which ruins your distance vision), and too much light above the cutoff shining into other drivers' eyes.

Also avoid the blue tinted "xenon lookalike" bulbs. The blue tinted glass filters out light, which can only reduce the output (a filter will never add light).

Your best bet is to go with a premium halogen bulb like the Philips X-Treme Power (I believe your bulbs are 9003/HB2, but it's best to check your manual or pull your bulbs out and check the number on the base before buying). These bulbs use a more precisely placed filament to get a better beam pattern (they don't produce much more light than a normal bulb, but they help your headlights throw it down the road better). They do have a small blue ring, but the filament is surrounded by clear glass so it's not blocking most of the light like a completely blue bulb would. I'd also normally recommend a relay harness (connects the headlights directly to the battery to increase voltage), but given the sensitivity of Mercedes electrical systems I'd be cautious about monkeying around with them.

You might also consider polishing or replacing your headlights. As the lens gets cloudy with age, their light output is drastically reduced. Here's a site with a lot of good information. Before you do this, know that polishing the headlights will remove the UV protective coating from them, causing them to yellow much faster. You'll have to keep applying sealant (included in most kits) to keep them looking new.

Lastly, if you really want HID's and have a lot of patience, you can retrofit HID projectors into your car's housings (meaning cut your headlights apart and put a HID projector from another car in there). Unlike putting rebased HID bulbs into your stock housings, a projector retrofit will give you a complaint beam pattern, but it's not easy. Here's a site with parts and information.