Third brake lamp malfunction

[C250CDI]

Dear all,
Re: w204, c250CDI, 2009
The 3rd brake lamp (the auxiliary stop lamp) has a malfunction. Sometimes is working perfect, sometimes not. The LED bar is fine, I suspect a relay, module, fuse or an imperfect contact. Where can I find the schematics for electrical circuit of the auxiliary stop light (3rd brake lamp) ?
Thank you!

 

[markmifsud]

what about a break in the wire near the boot hinge area?

 

[KillerHERTZ]

what about a break in the wire near the boot hinge area?

They are in the back window on a W204

Id start with the actual unit, disconnect it, look for anything obvious and then follow the loom from there.

 

[C250CDI]

Thank you for your support.

The car is sedan, not estate.

I removed the percel shelf .Underneath the wires, the connector and the LEDs appears fine. Using a tool to measure the voltage is 0. No voltage at all when I am pressing the brake pedal !!!
The wires I can see arround the trunk are fine. The problem is somewhere before the trunk (before the lamp and the last connector).

The 3rd brake light has a separate circuit, it is not the same for the tail lamps. Do you have a diagram for it?

 

[Alps]

it will go into the rear SAM - there may be a dodgy connection there.

 

[C250CDI]

The SAM appears fine.

 

[C250CDI]

I solved the problem by replacing the lamp. I bought a SH one from eBay, cost 60Euro. Works well now! Thank you all!

 

[dddooommm]

I had this issue when I replaced the front Sam unit!