Brake light - rear - driver side - WTF?

[Andle]

Hi all,

Rear lights: Side lamps & brake from the same bulb.

If I turn on side lights - both side rears come on. When I press brake, only the pass side side lamp bulb brightens further.

The driver-side only remains at sidelamp brightness. It does not get brighter upon braking.

Checked fuses - they seem fine. What else could it be?

Mot is due tomorrow! Help!

Andle.

[wheeler]

A failed bulb?? Sorry if that sounds obvious but you haven’t mentioned that you have checked or replaced it.

[GiveMeABreak]

Ditto^ and if you say they are new bulbs - regardless, check to see if the filament is wobbling about in the bulb - won't be the first, second or last time I've seen this with new bulbs - they get dropped on the shop floor and bashed about and can sometimes break.

[Andle]

When sidelamp on - the bulb is working. When the brake is pressed - the same bulb should brighten further.

Unless these bulbs have two filaments (and only one is gone) - i am flummoxed.

[wheeler]

Unless these bulbs have two filaments (and only one is gone) - i am flummoxed.

Thats exactly what it will be, a twin filament, some manufacturers like vauxhall do use a single filament bulb & apply different voltages for different brightness. Im not aware of Citroen doing this. Be aware that a twin fillament bulb is only designed to be fitted one way, if you have to force it then it is in the wrong way.

[admiral51]

Swap the passenger working correctly bulb with the drivers side bulb, if the passenger side bulb works in the drivers side then the bulb you took out is faulty

[white exec]

You've probably lost a Ground connection at the rear light cluster.
This can cause all sorts of odd behaviour, especially with twin-filament lamps.
Check Gnd connections, and make a new one if needed.