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E61 tailgate wiring - identify same colour cables - third brake light not working

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Hello All,


I just replaced all the cables on my tailgate but ran into an issue.


The cables on the right side were already cut and thus I ended up with three brown cables that I could not link to their corresponding ends. 

One was easy to figure out because it is thinner and connects the glass micro switch. 


But I still have two identical brown cables which I need to connect.

The 3rd brake light does not work. I tested it with a 9V battery and the LEDs are switching on which means the lamp is ok.


For the second brown cable I do not know what else is not working. It goes into the module on top of the tail, wide connector on the right side.


Any idea how to identify which cable goes where?

Are they maybe both the ground (minus polarity)? This is a test I still want to do, test the lamp with the ground coming from the car body. 


Any other ideas please of what I could do to identify the cables or how to fix the 3rd brake light?

Do you know if there is a wiring diagram available for all the cables going through the hinges and the systems depending on them?


Thanks a lot for your help and comments. 


Once this is fixed I will work on to the next issues:

- micro switch broken (glass pops by itself at start)

- right mirror dead

- left mirror intermitently dead (not answering any commands)


I like the car a lot but I am quite dissapointed with the quality and hate being ripped off by the garrage.


Thanks again


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Plain brown are earth, some have a pinstripe and this caught me out and I got 2 wrong, but it was the boot lock and a light.


3rd brake light is prone to failure so check for 5v on the wires running to it.

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Thanks a lot GoNz0I got the two browns connected. 


There is no voltage coming on the wires of the 3rd brake light. I guess the (+) is somewhere disconnected or it does not get any signal when hitting the brake. 


Anybody ran into the same issue?

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Big thanks Clavurion, 


Z13 was the problem. Quite difficult to detach due to the hard accessible screw.

Measurements were confusing but I guess normal with a broken Z13. 14V coming into Z13 when pressing the brake pedal. With the Z13 connected 12V outbound constantly at the black/yellow and brown wires, whether the pedal is pressed or not. 


It was out of curiosity that I opened the box. Twist with a wide screwdriver on each of the 4 corners and it pops out.

The damage was obvious, probably due to the shorts between the broken wires. Easy repair with a bit of soldering. See photos. 

3rd brake light works now. (The glass still pops by itself but the micro switch is ordered, on its way.) 


I noticed also that the cable (thick red with white strip) going into the other filter (Z402) is pretty cooked (see photo). I will have a look and at least place some isolation around. 

Good to check when one replaces the tailgate wires. 


Thanks for the great info on the forum and the feedback on my post. Very useful and much appreciated.







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I dropped the roof liner, not much space via the speaker openings and those f****** screws are too long. Fortunately, both suppressor and anti trap parts were ok.




A sign of someone else has been. I had to fix those clips with RTV and gaffer tape.


IMG_20180822_171700_zpsbamqlcrx.jpg     IMG_20180822_171649_zpsxepmeisp.jpg    IMG_20180822_173922_zps8gfu4me4.jpg

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Third brake light not working on my -08 525 XDAT. Changed all the wiring running through the hinges of the rear hatch last year. The LED lamp itself is tested ok, and the noise supressor Z13 is replaced OK. Suspect a wiring fault following me changing the cable bundle last year.

Does anyone have a guide to dropping roof liner in the rear?

Does anyone have a good wiring diagram for the third brake light?

Which fuse protects the third brake light?

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