I had a low beam warning and saw that the HID light on the left was not working, I read there isn't a fuse and that it can only be the bulb? Then I ordered bulbs (4) and changed them and it still does not work. Now I read that it is 90% chance that the ballast is faulty, according to some pictures it looks like the ballast is mounted below the headlight? I don't want to order a ballast and then it's a simple fuse or something silly. There's a 100 threads on fog light HID retrofit but nothing on the standard lighting system which I can find. Some assistance will be appreciated. Thanks

No?

I have the same issue as we speak. Hid bulb was changed on the left side and still have the low beam message. Where did you buy your bulbs from? Were they the cheap ones from eBay? Did you try swapping out the right side and putting it on the left side? Mine works from time to time. I haven't tried taking out the right side and inserting to the left side yet.

Yes they were ebay cheapies but they work fine on the other side. I noticed some moisture in the lens when pressure washing the vehicle so i dont know if this moisture has access to the ballast? I need to strip it but it seems like a job cause you need to remove everything around the headlight to get it out, bumper, grill etc.

Hello. I am experiencing the same thing. I already replaced the lamp to no avail. Now I want to swap the ballasts to confirm the problem. Can anyone point me to where the ballasts are located? An image or diagram? Thank you in advance. E

The ballast is on the bottom of the headlight housing. There's some good YouTube vids on it. A replacement ballast is not too expensive btw.

You say it works from time to time so could be a poor connection. Mine was totally stuffed so had to change it. Make sure the part number is correct as I now have an active lighting inoperative message everytime I start the car, goes off by pushing the OK button but still not ideal, although the headlight works perfectly. Like maximus said, it is below the headlight casing. It has 3 torx screws that hold it in place onto the bottom of the headlight. Not such a difficult job as it seems watching the videos to remove the headlight.

You hit the nail on the head when you said MOISTURE...They way our lights are designed the ballast is mounted to the bottom of light facing up into the light..The braided cable that runs to the bulb also runs down through bottom of light into ballast...With this being a
said it doesn't take but a very little bit of water to follow that braided cable down to the connector and when you fire up the low beam it shorts on the 25kv output side...Now it does have an internal circuit breaker that MUST see you turn key to off and remove from ignition to reset, but after it does this a few times the odds of burning out the ballast go up steeply....I retrofit and tune w204 headlights all the time and have seen this again and again....Easiest preventative step is to open the low beam cover and throw in a couple packs of desiccant...ive got prolly 10 bad ballasts for w204 in my shop right now



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