Canbus / towbar wiring Passat B6 estate

**pp241** · 19-07-2007,04:58 PM

Passat B6 140tdi manual estate

Hi is there anybody out there who can help please ??????????????
Like many others I am not prepared to shell out the silly money for a genuine VW towbar & electrics and have gone down the aftermarket route via Towsure. Apart from half dismantling the interior to get the rear bumper off (far easier on my old B5), the towbar was a dream to fit. Even from Towsure the plug-in wiring kit was over £100 (the fixed towbar was only £119!)so I went for their 7 way bypass relay at £26.99.
Now for the question - to save time does anybody know what colour wires to tap into for the tail, brake and indicators. Also I am thinking of tapping into the 12v socket in the boot for the 12v feed to the bypass relay and using an inline fuse (not sure where to put it for easy access but will report back when I've sussed it).
Over to you guys ! ! !
p.s. the plastic threaded studs holding the rear lights in are fragile but good news are only 40p from VW ! ! !

**Ben** · 19-07-2007,07:50 PM

First of all, welcome to the forum.

Can't help with the wiring issue, but if you wish to add some photos of you work etc and also, why not take a read of my towbar research, linked in my sig

**PNS2007** · 19-07-2007,09:20 PM

Hi there, you are braver than me in attempting this. I researched this before I had my towbar fitted and contacted no end of fitters both national and small local independants (inc towsure). See my thread in this forum.

You should not need to tap into any wires as the model specific wiring kit should plug in somewhere (so I was told). I would strongly suggest that you do not tap into any wiring from the loom as the vehicles wiring is quite sensitive and uses a cambus type system which should not be touched unless you know what your doing (plse accept my apologies if I'm wrong on this assumption). The passat also uses a trailer stability program which should be activated by a VW dealer which amounts to changing some codes in the engines computer. I personally would be very wary of medling with the electrics as you will void your warrenty and it could cost you a packet. Good luck though and I hope you succeed. Let us know how you get on. Neil

**pp241** · 19-07-2007,10:21 PM

Thanks for the welcome, I did read your towbar stuff - very interesting too. It seems to me that the hardware is the easy bit. I've been fitting towbars to my own vehicles for over twenty years and this is the first one that has stumped me. My trade is an engineer and I worked as a fork truck engineer for 6 years and stayed in the industry after I came off the tools for a further 12 in various roles. Canbus technology came onto lift trucks about 8 years ago, too late for me though. I spoke to a fitter at Towsure in Sheffield who has done a new Passat but his notes are now somewhere in the North Sea ! I am determined not to give up and will post the result !

**pp241** · 19-07-2007,10:39 PM

Thanks for the post Neil, as I said I refuse to be held to ransome by VW who would get my money if it priced the plug in kit resonably. Canbus is not such a mystery as I said I do have a rudementary knowledge just need to have it explained in more detail. I think the system basically uses common wires for several functions and sends different voltages (just a few volts in many cases) to trigger the things connected to them. All the bypass relay does is sense these voltages and with the aid of a 12v supply into the relay sends a 12v output to the relevant function on the trailer / caravan. With regard to the vehicle management system yes you are right re warrenty it could be a problem. My last B5 (130 Tdi sport) had ESP as well but had no way of telling (as far as I know) when I was towing. The one big issue which I can see the need for the management system to know about is the electronic handbrake which possibly would need putting on a little more strongly.
I will let you know if I get through the minefield.
Cheers Paul

**pp241** · 02-08-2007,07:34 PM

Not that it's of much to you now but thought I'd update you on my story. The bypass relay picks up the small canbus voltages to the various light functions and by way of a 12v fused supply routes 12v to the towbar socket and so on to the trailer/caravan/jetski etc etc. Anyway after much tooling around I got hold of a vehicle wiring diagram picked up the relevant wires tapped into the boot 12v socket via a fuse and tested the socket which seemed to work. Flushed with sucess I clipped all the trim in and drove to my caravan storage pound, backed up to it plugged in and kept my fingers crossed - it worked! ! ! The cost of the WK5 bypass relay is £29.00 so I guess it was just about worth the aggro ! !