MB Medic Mercedes-Benz Repair Guides, Service, How To DIY
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In this guide (5 sections)
Many Mercedes-Benz cars still come with halogen light bulbs. The halogen bulbs can be easily upgraded to HID (Xenon) headlights for brighter light and a more modern look. Factory HID systems do give better light at night, but a conversion kit fitted into a housing built for halogen is a different proposition, for the reason set out immediately below. If HID low beams are not standard on your Mercedes-Benz, you can always get an aftermarket HID Conversion Kit. We recommend getting a kit that is ERROR-FREE with a slim design to avoid any defects and warning lights on your instrument cluster. If the HID kit uses 55W, you shouldn’t get error messages on the instrument cluster.
The federal position is not ambiguous. In an interpretation letter on exactly this question, NHTSA concluded that it would not be possible for an HID conversion set to meet the photometry requirements of a system built for halogen, that such lamps could not be sold for that purpose, and that a dealer or repair business could not remove the original halogen headlamps and fit HID replacements, citing the federal prohibition on making safety equipment inoperative.
So treat this guide as what the notes further down already say it is: a procedure for off-road, racing and show use. If what you want is better light on the road, a projector retrofit or a better quality halogen bulb gets you there without creating glare for everyone else.
Best rated HID conversion kits for a Mercedes-BenzÂ
- HID Conversion Kit H7, error free slim design, on Amazon
- Conversion Xenon Kit for Mercedes-Benz Slim Design on Amazon
One of the best HID Kits for Mercedes-Benz, with great reviews from MB owners, is the MTEC HID Conversion Kit on Amazon. The kit is easy to install, has authentic ballast and bulb, and works great on MB cars. Â The downside of this kit is that it’s more expensive than most HID kits you find online.
You can choose any color for the HID bulbs. We recommend either a 5000k, which is white, or a 6000k, which is slightly blue. If you go higher than that, the light turns blue at 8000k, and at 12000k, the light output is more of a purple color. The problem with the blue and purple light is that visibility is reduced at that light spectrum. The choice is yours.
Instructions on how to upgrade the Mercedes-Benz light to HID Xenon
The following instructions are for installing HID lights on a W204, but these instructions are similar to those for other Mercedes-Benz cars without HID headlights. That’s because Mercedes-Benz used a H7 halogen light bulb, and the mounting of the bulb is similar in other models such as the E-Class, CLK-Class, ML-Class, CLS-Class, C-Class, SL-Class, etc.
In addition to an HID Conversion Kit, you will need electrical tape, a flat screwdriver, and a razor blade.
IMPORTANT NOTES:
- Installing the ballast inside the headlight can cause damage to the headlight assembly. Only install your HID this way if your ballast doesn’t produce too much light. Keep the ballast outside for a safe installation. Watch the video below to install the ballast outside the headlight assembly.
- Installing the HID Conversion Kit can void your Mercedes-Benz warranty.
- The only HID systems that are road legal are the ones engineered into the car at the factory. Note also that a “DOT” marking on a kit box is the manufacturer certifying itself, not an approval issued by the Department of Transportation. There are no DOT-approved HID conversion kits. Therefore, HID conversion kits are for off-road, racing, and show car use.
Step 1: Open the Hood
Start by opening up the hood. The hood release is on the driver’s side, underneath the dashboard.
Step 2: Access the back of the headlight
Remove the cap from the back of the headlight assembly. To remove the cap from the back of the Mercedes-Benz headlight assembly, you must twist it counterclockwise. Â You may want to wear gloves as you perform this upgrade.
Step 3: Remove the old bulb
The bulb can be easily removed by twisting it a few degrees. Pull out the H7 halogen light bulb. 
Remove the electrical connector from the headlight and pull the H7 bulb out of the socket.
Step 4: Install the HID
For a clean install, we will insert the ballast inside the headlight. This way, we avoid drilling holes in the headlight assembly. Use a Double Sided Tape, such as 3m to place on the bottom of the ballast. Once you do that, insert the ballast inside the headlight housing and make sure it is secure. If your ballast gets very hot, you could risk damaging the headlight assembly with this method. 
You may want to test your ballast before installing it to ensure it doesn’t get too hot. You could also install the ballast outside the headlight, but you will need to drill holes in that case. It would be best if you were careful when handling these light bulbs, and also, don’t touch the ballast or bulbs when the lights are on.
Step 5: Make wire connections
You must insert the wires through the metal clip that locks the bulb in place, and you must remove the rubber piece to do this. 
In our case, we cut out the rubber piece. We don’t need it since we installed the ballast inside the headlight. If you plan on installing the ballast outside the headlight, you will need this rubber piece and will need to drill holes in the headlight assembly.
Step 6: Make the Ballast Connection
Now, plug the HID Xenon Bulb into the HID kit. The wires are specifically designed so that they can not be mixed up. 
Check out a picture from our installation. Shown out of the headlights to demonstrate how the wiring should be set up.
Step 7: Install HID Bulb
Install the H7 HID Xenon bulb into the headlight assembly. This can be tricky because you can’t see the socket. Here are some pictures that should help you install the H7 HID bulb.
Step 8: Connect to the stock H7 socket
Now you need to feed 12-volt power to the ballast. Connect the two wires from the ballast to the H7 plug you removed from the halogen light bulb. Go ahead and try your new lights.
Video: DIY HID Xenon Install: Mercedes-Benz C-Class 250/350 2007-2014
If you plan on installing the ballast outside the headlight assembly, you may follow the following video for help. Besides installing the ballast outside the headlight assembly, the H7 bulb clip is a different design on this C-Class.
Frequently Asked Questions
HID Conversion Kit Problems
Certain HID Conversion Kits may not work well with Mercedes-Benz electrical systems. If you purchase a low-quality kit, the lights may flicker or flash when you turn them on when the engine is on.
Will an HID Conversion Kit Void my Warranty
If your car is still under warranty, making unapproved upgrades, like installing an aftermarket HID kit, could void it. Check with your MB dealer to verify whether your car is still under warranty.
What is HID?
HID stands for High-Intensity Discharge. It uses a high-voltage charge of electricity from the ballast to arc between two electrodes inside a bulb full of different gases.
How long will my HID bulb last?
HID bulbs last around 5000 hours.
How much power will the HID Conversion Kit use?
HID Conversion Kits use ballasts that draw 35 watts of power. Mercedes-Benz halogen bulbs draw at least 55 watts. The HID Conversion Kit does draw slightly more power at start-up.
If the dashboard reports a bulb failure afterwards
This is the most common complaint after a conversion and it is not a wiring mistake. These cars measure the current the headlight circuit draws to decide whether a bulb is alive. A ballast does not draw current the way a filament does, so the car reads a working light as a dead one, which is what the error free kits mentioned above are trying to work around with a resistor or a capacitor.
Two things follow from that. A kit sold as error free is making the car stop complaining, not making the installation correct. And if the message appears anyway, a full system scan will tell you whether the car has logged a current fault or is holding a stored one from the swap, which is the difference between a wiring problem and a message that simply needs clearing. The YOUCANIC UCAN-II Pro reads and clears the body modules that hold bulb monitoring, which a basic OBD-II reader cannot reach.
Related reading
Before you buy parts, scan every control module, not just the engine. It shows the root fault behind the warning lights and tells you whether the problem is still active. See how to do a full health check.
