Trailer brake signal issue (Red trailer wire to CJB/BCM)

[gotaflat]

Morning...

I have been investigating an issue with my non functioning trailer brakes that were disconnected at some point (wife's car).

Basically I re joined the cut wires in back of the car and tail light assembly with new diode - as the D4 brake instructions but have this conundrum which there is no signal/power for the red wire as marked in yellow below [bighmmm]:


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This means the controller is not getting the trailer brake signal and not giving me the green light /or red when brake peddle touched. = no trailer brakes.

Assuming the red line should be + in some power/volts ? - at the moment MM is not giving me any on the reading. ? I was sure the blue was giving me some power 4+ but need to re check.

I traced back to the inside left of the car and the trailer 'socket' and tried to get a read - but seemingly 0 .

At this point I can only assume the line is damaged somewhere back to the CJB? or the CJB/BCM is damaged?

A replacement CJB/BCM feels bad and over the top .....but surely this can diagnosed? or if there is better area to access to test that cable ?

On thinking back - this may have been damaged when the rear air con condenser was replaced? as that area got pulled out ... unfortunately I don't drive the car much and don't see these things until its an issue.

Any help appreciated.

[gotaflat]

Updated.Checked power in the fuse box for any trailer related feeds

Number 27 (trailer side lamps) = 0.0v ???????
48 (Trailer connector Trailer feed) = 12.04v
54 (Trailer connector Ignition feed) = 12.04v

So looks odd . But i am also getting this on the reverse screen ... like a trailer is connected... and no reverse sensors (front yes). did not get this before I reconnected the brake controller
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However more disturbing is the taped wires in there... WTF is that???

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At this point happy take it some someone that can straighten this out...

[josh.huber]

Do the brake lights work on the car?

[gotaflat]

Do the brake lights work on the car?

Car yes - have not checked trailer when hooked up yet

[josh.huber]

If there working the signal from the cjb should be fine

[Tombie]

Updated.Checked power in the fuse box for any trailer related feeds

Number 27 (trailer side lamps) = 0.0v ???????
48 (Trailer connector Trailer feed) = 12.04v
54 (Trailer connector Ignition feed) = 12.04v

So looks odd . But i am also getting this on the reverse screen ... like a trailer is connected... and no reverse sensors (front yes). did not get this before I reconnected the brake controller
183051

However more disturbing is the taped wires in there... WTF is that???

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At this point happy take it some someone that can straighten this out...

The blue tape is factory over crimp joints.. Dont worry about it too much.

[gotaflat]

If there working the signal from the cjb should be fine

yep ok understand,

Thats for the car right - is the trailer plug a separate feed/plug? straight from the CJB (according the diagram)? Because that red line has 0.0v (may be an initial 0.02v) but zippo - i cant explain that - i am sure that needs to have a signal (can potentially run a wire with diode to the car brake light.. but ....)

I can only speculate that there may be crossed /exposed wires down to the rear 6 pin round socket? that why the car thinks there is a trailer on once the trailer brake (blue to Brown trailer wire) is joined??

[josh.huber]

yep ok understand,

Thats for the car right - is the trailer plug a separate feed/plug? straight from the CJB (according the diagram)? Because that red line has 0.0v (may be an initial 0.02v) but zippo - i cant explain that - i am sure that needs to have a signal (can potentially run a wire with diode to the car brake light.. but ....)

I can only speculate that there may be crossed /exposed wires down to the rear 6 pin round socket? that why the car thinks there is a trailer on once the trailer brake (blue to Brown trailer wire) is joined??

What yr and model is it

[gotaflat]

What yr and model is it

2011 - SDV6 3.0 HSE

[josh.huber]

Turn the indicators on, one at a time and see which one if any bring on the flashing icon on the dash that lets you know the trailer lights are working.

[josh.huber]

yep ok understand,

Thats for the car right - is the trailer plug a separate feed/plug? straight from the CJB (according the diagram)? Because that red line has 0.0v (may be an initial 0.02v) but zippo - i cant explain that - i am sure that needs to have a signal (can potentially run a wire with diode to the car brake light.. but ....)

I can only speculate that there may be crossed /exposed wires down to the rear 6 pin round socket? that why the car thinks there is a trailer on once the trailer brake (blue to Brown trailer wire) is joined??

Does it behave the same with the brake controller connected?

Yeah I just checked they both come from the JB separate, I was wrong, thought they were joined at rear.

Check fuseable link 18.

Need to see if the trailer lights work, but that would only be the red wire anyway.

I'd check all the breakers attached to the cjb. But if work has been done in the rear. I'm going there first