trailer wiring

[apersson850]

Aha, so they have some kind of buffer device? But not a real one, since it seems to still tap into existing wiring, to know if the brake light (maybe all lights?) are on or not? Now when you explained it in more detail, I think I get what you meant in the previous posts. A "loom", is that what some call a wiring harness? Although my English is decent for not being a native English speaker, that are some of the more unusual expressions that are difficult to dechiper sometimes.

The proper module gets this information from the CAN-bus in the car.

Then what you don't get with a simple buffer device is the monitoring of the lamps on the trailer, automatic cut off of the rear fog light on the car when a trailer is connected, automatic auto stop cancelling with connected trailer, disabling of the rear parking warning devices and such stuff, I presume?

Watch out for the brake light connection. You aren't the first one who have tried doing it like this, instead of the proper way. Several didn't get the brake light to work at all, because they were measuring voltages for the brake light, to find the proper wire that way. But when you do that, you have the tailgate open. These cars don't illuminate the same brake light with the tailgate open as when the car is driven with the gate closed.

[realslimshady]

yes Mr Apersson, you are correct with everything you have said.
I have connected a 'jumper' wire from the actual brake light connector in the hatchback to the module and the trailer brake lights work. My problem now is that the wire at the connector is violet/brown as suggested by a previous contributor, but there is no violet/brown wire in the loom where it appears behind the fusebox in the l/h corner. So either the loom goes somewhere else, or the two brakelight wires are spliced into a different coloured wire.
The investigation continues....

[realslimshady]

Finally found a diagram online, which told me the brakelight wire originates as grey/brown in the loom. But there are two grey/brown wires. Guess what? One of them doesn't trigger the brake lights. And which one did I splice into first? However.
All working as it should now, and car is not complaining.

[Tony Rama]

Originally Posted by realslimshady

Finally found a diagram online, which told me the brakelight wire originates as grey/brown in the loom. But there are two grey/brown wires. Guess what? One of them doesn't trigger the brake lights. And which one did I splice into first? However.
All working as it should now, and car is not complaining.

Sorry. My mistake about the Green/Brown. I misread the abbreviation. GR for green, when GR should be grey. Fog light looks like White/Blue.

For other's info. a loom is a whole load of wires bunched together by tape or some other kind of binding.

Also the kind of module in question only takes micro amps so does not disturb the vehicle's light warning system. Some of these modules also give a warning sound if a trailer bulb is out. They are well worth it for about £20.

[realslimshady]

Thanks for your help Tony.
Yes, the 'black box' came with the towbar kit and is working fine, only complaint is there is no buzzer when the indicators are operating, but I can live with that, it's only for occasional small trailer towing.
Cheers

[apersson850]

This is one of the issues with using a non-standard connection. The TRM will provide brake lights to the trailer regardless of when you press the brake pedal.
But there are three separate brake lights on a 2010. The top brake light in the window, the high brake lights to the side and the low brake lights at the same position as the tail lights.

During normal driving, the car will use the top lights at the side (grey/brown before connector 74/602:3, then black and after splice 73/6002 violet/brown) and in the window (yellow/gray before connector 74/602:2, black after).
But if the tailgate is open, it will instead use the low brake light (grey/brown both before and after splice 73/5089).

This should sort out your confusion, I presume.

So a connection to just one of them will not provide the intended functionality. Plus you lose the auxiliary functionality of the real TRM.

I'm glad I got the real thing.

[spitz]

Originally Posted by apersson850

Watch out for the brake light connection. You aren't the first one who have tried doing it like this, instead of the proper way. Several didn't get the brake light to work at all, because they were measuring voltages for the brake light, to find the proper wire that way. But when you do that, you have the tailgate open. These cars don't illuminate the same brake light with the tailgate open as when the car is driven with the gate closed.

So glad I found this thread as I have the exact same problem. Trouble is it only came to light at MOT time when my car was initially failed. Fortunately the tester allowed the car to pass when I explained I was only using the tow bar to attach a bike rack.

I never spotted the problem when the tow bar and electrics (3rd party non Volvo) were initially fitted as the brake lights on the bike were checked with the tailgate up!

Is there any known way of fixing the brake light issue, by for example, splicing into a different wire? I’m concerned I won’t be treated with the same leniency as I am having my car tested a different location to the previous test.

[spitz]

The first picture shows the bypass module fitted when I had the tow bar and 13 pin electrics installed. The red wire at position 6 goes to the brake light pin on the tow bar socket. There is voltage present when the tailgate is up and brake pedal pressed, but goes off when the tailgate shuts.

The second picture shows a red wire leaving the bypass module and I think going up into the light rear light cluster that sits below the tailgate.

Thanks for any help and advice!