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Taillights too bright

bulbs the wrong way round (if they are dual filament)

or a sticky brake peddle switch
 
bulbs the wrong way round (if they are dual filament)

or a sticky brake peddle switch
Not sure about the brake peddle switch as the brake lights works fine. Bulbs are correct placeand correct wattage
 
This is very strange.

When I look up the tail lamp/brake light bulbs for my C180 it says 2 x P21W. That's a pair of single filament bulb each of 21W. How can they use bulbs of the same brightness for both tail and brake light. Well they can't as it wouldn't be permitted. My conclusion is either the data is wrong or the car uses some electrical trickery to reduce the brightness of the tail lamps vs the brake light. If that is the case then my wild guess is the tricksy bit may have failed on the OP's car.

Why make it simple when they can make it complicated.
 
Isn't 5w the legal max for tail lights, 21w for brake?
 
Yes I expected to see 5w or 10W (even my old 190e had 10W tail lights) but I've tried 3 or 4 different bulb finder sources including an owners manual and they all say 382 or P21W which is a single filament 21 watt bulb. In fact with the exception of the number plate bulb every bulb at the rear is a P21W, that's brakes, tail, indicators and fog. Some logic in that approach I suppose.

I'm curious enough now to inspect my bulbs when I get home.
 
My conclusion is either the data is wrong or the car uses some electrical trickery to reduce the brightness of the tail lamps vs the brake light.
The W204 does, indeed, use trickery to reduce the brightness of the tail lamps in normal running. Under normal circumstances, the car runs the 21W tail lamps at reduced voltage / brightness.

The trickery has two functions to deal with bulb failures: In the event that a brake lamp bulb fails, when operating the brakes the tail lamp bulb in the same cluster runs at full voltage so that you have a brake lamp on both sides of the car; similarly, if a tail lamp bulb fails, the brake lamp bulb runs at reduced voltage so you still have a tail lamp showing in the same cluster.

In addition, if the car is in reverse and the reversing lamps are illuminated, when you operate the brakes the regular bake lamps illuminate, and the tail lamps also illuminate at full voltage making the overall brake lamps brighter so they are still visible “over” the white reversing lamps.
 
I had a W204 saloon which had issues with the rear lights. Have a look at the plastic connector as, the 204's burned out and gave a useless Earth. This cretaed one side brighter than the other.
Mercedes know this is an issue but refused to treat it as a recall. If addressed by the customer, they generally replace them FOC.

Worth checking
 
^ Good call - I’d forgotten that particular issue.
 
The trickery has two functions to deal with bulb failures: In the event that a brake lamp bulb fails, when operating the brakes the tail lamp bulb in the same cluster runs at full voltage so that you have a brake lamp on both sides of the car; similarly, if a tail lamp bulb fails, the brake lamp bulb runs at reduced voltage so you still have a tail lamp showing in the same cluster.

In addition, if the car is in reverse and the reversing lamps are illuminated, when you operate the brakes the regular bake lamps illuminate, and the tail lamps also illuminate at full voltage making the overall brake lamps brighter so they are still visible “over” the white reversing lamps.

There is method in their madness then.

I had a W204 saloon which had issues with the rear lights. Have a look at the plastic connector as, the 204's burned out and gave a useless Earth. This cretaed one side brighter than the other.
Mercedes know this is an issue but refused to treat it as a recall.

It was a recall in the US on safety grounds. From what I've read it was a bigger problem in US perhaps due to their habit of sitting with the brakes lights on for long periods. Knowing the earthing is not up to the maximum current that can flow is one reason why I always avoid holding the brakes lights on at traffic lights or other hold ups. Thanks st13phil, you've now given me a reason not to hold the brakes lights on in reverse which sounds to be an even worse scenario for the earth cable to deal with.
 
Hello and thank you all for your replies and your help..
The problem was using the wrong bulbs wattages. The taillight bulbs should have been 4 watts double felement. All the bulbs specifications are printed on the back of the plastic plate where the bulbs fits. Also, I had to change both of the plastic plates because where the bulbs fitted they were loose.
Final note, If you need bulb replacement go to Mercedes main dealer or someone who knows what they are talking about as I was sold some bulbs from two top car parts companies and the fittings and wattage were diffrent and they wouldn't take them back.

Thank you all
 
Glad you got it sorted - cheap and easy fix as well ;)
 
The earth burning out was an issue on BMW 3 series from around 2002 to the present day.
Also a lot of newer Mercedes have a hold feature which holds the brake and brake lights on without applying the handbrake.
 

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