Genuine Volvo Trailer Harness Problem.

[S60D5-185]

Hi, I have recently fitted a Towbar to my 2007 XC90 and today went to install the Volvo Trailer Harness and Module which I bought new.

I have used these harnesses on 3 previous occasions with other Volvos that I have owned and never had the slightest problem

I've just finished installing it all and as per usual it has gone together very nicely, HOWEVER for some reason, the brake lights are not working on the trailer. They do illuminate on the car.

The trailer brake lights are fine and fault free as the brake lights do work correctly when I couple it to my XC70 which is also fitted with a Volvo harness and module.

Fuses are installed in position 7, 20, 29, 30 .


Any ideas please ?

[Harley Dave]

7 pin or 13 pin?

Cheers

Dave

[Harley Dave]

Forget that - must be 13 pin with 4x fuses - Right?

I can only think that the black plug into the fuse board is not seated correctly (or the trailer module is faulty...)

You could swap the module from the other car and see what happens?

Cheers

Dave

[S60D5-185]

Yes 13 pin Dave, unfortunately my XC70 has just driven off with the new owner.

I will check the connections again as I have never had the slightest problem with these in then past.

[SwissXC90]

With a multimeter check the following:

13pin Tailer Plug
Pin 6 = brake lights
Pin 3 = ground
Pin 13 = ground

Pins 3 and 13 are connected together in the wiring loom and so you must measure 0 ohms between 3 and 13, and 0 ohms to ground

TRM Trailer Module Connector
A10 ground (black)
A6 & A12 (red) +12V from REM fuse F29, 25A, feeds TRM left indicator and taillights
A7 & A8 (red) +12V from REM fuse F30, 25A, feeds TRM right indicator, brake lamp and fog lamp

It's gotta be a simple problem.

[S60D5-185]

Originally Posted by SwissXC90

With a multimeter check the following:

13pin Tailer Plug
Pin 6 = brake lights
Pin 3 = ground
Pin 13 = ground

Pins 3 and 13 are connected together in the wiring loom and so you must measure 0 ohms between 3 and 13, and 0 ohms to ground

TRM Trailer Module Connector
A10 ground (black)
A6 & A12 (red) +12V from REM fuse F29, 25A, feeds TRM left indicator and taillights
A7 & A8 (red) +12V from REM fuse F30, 25A, feeds TRM right indicator, brake lamp and fog lamp

It's gotta be a simple problem.

Thanks Swiss, I was hoping you would be along.

I'll check it tomorrow with said Multimeter.

Many thanks.

[Harley Dave]

Well done Swiss

While we are on the subject, (and waiting for the next instalment from S60D5), I recently replaced my Volvo7 pin wiring with the Volvo 13 pin cable.

It just plugs into the trailer module and the fuse board (in my case into the existing "tail" as mine's an exec) and there were no issues.

Except...

There's a "spare" wire (white) taped alongside the new cable which looks like it could be inserted into the big connector in a similar way as I had to do with the 7 pin (to select charge or perm live etc)

Any idea what function the extra wire would give?

Cheers

Dave

[SwissXC90]

There are two spare wires on the 13pin trailer connector.
They're documented on the wiring diagram:

Pin 11: RESERVE: CHARGING COMMON RETURN
Pin 12: RESERVE: INDICATION TRAILER

[S60D5-185]

No update guys as life got in the way off tracing the issue.

Maybe tomorrow.

[Harley Dave]

Originally Posted by SwissXC90

There are two spare wires on the 13pin trailer connector.
They're documented on the wiring diagram:

Pin 11: RESERVE: CHARGING COMMON RETURN
Pin 12: RESERVE: INDICATION TRAILER

Thanks Swiss

I'm in Spain and don't have a 13 pin caravan here to test the charging and constant 12v pins but I do have a 13 pin bike rack with me but that doesn't use all the features of course - the lights all work OK on it though.

I'll get onto checking things out with my meter tomorrow, the instructions I followed (file is too big to be attached) did not mention the spare wire...

"Indication Trailer" sounds interesting - what does that do?

Is it an indication (in the car) of a trailer being connected or something else?

Cheers

Dave