Combined stop and tail light trailer wiring?!

[CornishPete]

Hi, I've fitted and wired a towbar to our 2012 insignia but got a slight issue with the wiring.
The brake lights on the insignia are combined stop/tail lights so when the car lights are on, the bulb lights up like a sidelight, then when the brakes are applied the same bulb gets brighter indicating brakes on, it's not a dual filament bulb. I've used a universal bypass relay as when I fitted a P F Jones vehicle specific wiring kit on our old car (meriva) it was basically a bypass relay with a few piggyback fuses and you still had to tap into the wires with scotch locks. Anyway, all other lights work fine but the trailer brake light now comes on when either the brakes are used or the lights are switched on! It's not differentiating between the two. I assumed one wire leading to the stop/tail bulb on the car carried two signals depending on the situation and the purpose of the bypass relay was to separate the two? Anyone have a solution?
Many thanks!

 

[Red'n'Black]

My Saab had a similar system, single filament for the tail lights, run at two different currents. Probably the same GM electrics underneath?

The towbar electrics needed a special module to go between the socket and the can bus. Plus software updates etc, not much change from 500 notes.

And after all that it wouldn't drive the LED lights on my trailer, wouldn't detect that they were there, had to go back to filament ones

 

[Keithmac]

Our Mk2 Kuga required a proper CanBus Trailer Module and coding.

 

[CornishPete]

You'd think it wouldn't be that difficult for manufacturers to install an iso plug behind the lights that you can simply connect the tow bar wiring into!
Cheers for the replies. I think I'll just leave it as it is for now. We never tow at night so during the day it all works fine and if we ever do have to tow at night the brake lights on the trailer will just be permanently on.

 

[hotponyshoes]

To do it on the cheap just run a single wire from the car bulb and replicate the dim/high function with a single filement on the trailer.
Will probably give you a warning on the dash.

 

[hotponyshoes]

You'd think it wouldn't be that difficult for manufacturers to install an iso plug behind the lights that you can simply connect the tow bar wiring into!
Cheers for the replies. I think I'll just leave it as it is for now. We never tow at night so during the day it all works fine and if we ever do have to tow at night the brake lights on the trailer will just be permanently on.

Some do.
Although it's normally a custom socket that they then sell a £200 loom for..

 

[Kayos]

I have a 2015 Insignia estate, with an after market towbar

I would look to see how they did it, but the car is both broken and not here. I'm hoping both of those are resolved soon and I will take a look

 

[m_c]

To do it on the cheap just run a single wire from the car bulb and replicate the dim/high function with a single filement on the trailer.
Will probably give you a warning on the dash.

That would likely trip the overcurrent protection for the bulb.

 

[hotponyshoes]

That would likely trip the overcurrent protection for the bulb.

Is there overcurrent protection on a 2012?

 

[hotponyshoes]

Just to check,
You haven't connected the side light wires from the relay to the car have you?

 

[bricol]

I got around a similar sort of issue on a US import (brake light also used as a turn signal).

Ran wires from the front indicators to the rear to trigger relays for rear/trailer indicators.
Another wire from center brake light to a relay to light the car and trailer brake lights.

So in your case it might be possible to run a wire from a front side light to a relay for trailer lights.
Center brake light to relay for trailer lights.

 

[m_c]

Is there overcurrent protection on a 2012?

Yes.
Pretty much anything using CAN bus for lighting will have circuit protection built into the module.

 

[hotponyshoes]

Yes.
Pretty much anything using CAN bus for lighting will have circuit protection built into the module.

I've done quite a bit of 'budget' wiring on canbus cars. Plenty of them show a bulb error on the dash when the trailer is connected but they don't normally stop the lights from working.
Apart from one which was a BMW mini (I think?)
And the interior lights on a Mercedes van which were a nightmare..

Anyway,
If the op has canbus the stop/tail bulb will probably have a pwm feed.

What he needs to do (to do it properly) is use a 'smart' / 'multiplex' bypass relay.
Do NOT connect either of the side light wires from the relay to the car.
Just connect the brake light wire from the relay to the stop/tail wire (+ side) on the car and make sure the +12v and - wires on the relay are connected.
Then feed the wires coming out of the relay to the separate stop and side circuits on the trailer.

There is a good chance the relay he has already bought is a smart one as its pretty hard to find the 'dumb' ones now..
Not much to loose by disconnecting the tail light wires and trying it..

 

[CornishPete]

Ok, an update. Wiring now fixed! I had indeed crossed the brake and sidelight wires ‍. The brake and left hand side light both have a purple wire leading to them. At the light cluster (pictured) it looked like the brake light wire has black marks on and the sidelight wire doesn't, distinguishing the two, so when I stripped a section of the protective tape in the boot area exposing a small section of the wiring loom and one of the purple wires had black marks and the other didn't, I assumed this was the brake wire.
Peeling more tape off the loom revealed both wires are purple with black marks on but the brake light has a thin grey stripe, on an already thin wire, which I just didn't see! You can just see it if you zoom in on the picture!! Swapped em over and all working fine now but I think I might just switch the scotch locks for wago connectors next time I get a minute!
Thanks for the replies everyone!

 

[Turbo]

Get rid of the scotchloks they are a botch job and always cause problems.