W203 C55 / W209 CLK - How To change HID dipped beam bulb

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Oct 19, 2020
S203 C55 AMG, Citroen e-C4, McLaren 570GT
A week ago, driving home in the dark, I got a message on the dash saying my left headlight wasn't working. The message went away and the bulb did then light up, but looking at it from the front, I could see it was noticeable purpler than its right-hand counterpart. Clearly needing changing, especially as I need to to drive somewhere on Saturday.

Consulting the manual, I was met with the information that the dipped beam is a HID operating at high voltage, and that I should consult my Mercedes dealership rather than attempt to replace it myself. Searching online, I became a little confused. My car is a C55, and thus has the front end of a W209 CLK. However not all CLKs have the HID lights. I was on the point of calling a garage, but decided to have a go.

In fact, unlike many modern cars, it's a fairly nicely designed setup that makes it reasonably straightforward to change a bulb. Given that, I thought I'd share a few pics, in case anyone else is put off by the warnings in the owners manual.

You will need:
- A Mercedes W209 CLK with HID headlights, or a W203 C55
- A D2S 35 Watt replacement headlight bulb (I got mine from Halfords for £35, an Osram which matched the dead one). It appears that any D2S bulb will fit, you probably want the same wattage.
- Daylight (or some very good work lighting) the first time you do this - much easier to see what's going on in daylight.

Before you start, turn the lights off (the '0' position on the dash switch), and remove the key.
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Pic of the lights I'm talking about - these are the W203 C55 saloon/estate, same as the second-gen W209 CLK I believe. The dipped beam lives in the outer headlight (the inner one has the main beam and the sidelight).
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Coming round the back we find the large round dust cap. It opens by twisting anticlockwise about one-eighth of a turn. These can be a bit stiff - don't be afraid to get a good grip on the outer rim and twist it open like a recalcitrant jam jar.
With the dust cap removed we see the power connector to the base of the bulb. This too comes off with an eighth of a turn anti-clockwise. It's a bit like removing a house lightbulb from a bayonet fitting, but here you're removing the fitting from the bulb rather than vice-versa. Mine both came off very easily.

With the power connector removed we see the base of the bulb itself. The bulb is held in place by the two wire clips you see below, which pivot left and right at their top end, and hook into a clip in the holder at the bottom end. You slide the lower end of each clip inwards towards the bulb to release it from the holder, it then swings outwards out of the way, releasing the bulb.

After unclipping the two clips, the bulb should be loose and come out easily, looking like this
The blackened mid-section above shows why this bulb is in need of replacement - a good bulb is clear throughout.
As it comes out, the larger square cut-out in the rim will be uppermost - you will need to insert the replacement bulb in the same orientation. (The cut-out that's pointing off to the left in this pic)

Insert the replacement bulb, holding it by the black base to avoid getting finger-grease on the glass surface of the bulb, which could shorten its life.

Refitting is the reverse of removal as they say - push the two clips inwards and then 'down' (into the light unit) to clip the bulb in, put the power connector onto the end of the bulb and twist slightly clockwise to get it back as it was, then twist the dust cap back into place (taking note of the 'top' logo on the back of the plastic).

Turn on your headlights, and come around the front of your car to admire your handiwork.
Interesting - thanks for this. My C320 Sports Coupe has similar headlamps.

Did you take any precautions re. the high voltage warning?
Interesting - thanks for this. My C320 Sports Coupe has similar headlamps.

Did you take any precautions re. the high voltage warning?

The only precaution I took was turning the headlights off and removing the ignition key ;-) And I'm still alive.

The power supply is delivered to the back of the bulb via the square connector. The actual electrical 'live' parts are well embedded in the socket of this connector. As far as I can see, you'd have to do something really silly to actually make contact with the live terminals in the connector - it's really easy to just hold the back of the connector and twist it to release, and then put it back again onto the new bulb. I.e. it's a big square plastic housing on the back which is easy to hold perfectly safely.

IMO the risks of changing your Merc headlight bulb with such a setup is probably lower than the risk of changing a regular 240V lightbulb at home, and I wouldn't pay a builder £100 to come and change a bulb in my living room :)

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