Audi A6 2013 Towbar wiring with bypass kit

[Bill Badger]

I've just fitted a detachable towbar to my 2013 A6 saloon. I usually fit a towbar to my car and always fit it myself. I've had no problem with the actual fitting, and all has been torqued up as per instructions etc. I didn't even have to make a cut to the bumper, which was an added bonus. My question concerns the electrics, and this is the first car that I've had that has me scratching my head with regard to connecting the bypass unit. Details as below:

1 - Bypass kit is made by TPE elektronik and shows various fitting options.

2 - I've realised that although the car has normal filament bulbs, the same bulb is used for both tail light and brake light functions by the electronics pulsing the signal rather than merely being 12V or 0v.

3 - Realising that I can't simply connect to each wire in the rear loom in the conventional way, do I wire it as Multiplex 1 or Multiplex 2 diagrams?



4 - Lastly, having the battery in the boot may be beneficial to easier wiring, but should I connect to the battery (via a fuse of course) or to the auxiliary socket wiring in the boot? I don't like the idea of connecting a relatively unknown circuit board across the battery on a permanent basis, but if I play safe and connect to the auxiliary socket wiring, the towing socket will only function when the ignition is on, thus not giving a parking light function....... I could put a switch in the system and connect to the battery, but there is the risk that I will forget to switch on when towing my trailer or using the bike rack!

Any suggestions?

Incidentally, the towbar kit was purchased on Ebay, and although the seller is technically in the UK, the towbar kit comes in directly from Italy. All EU quality and test requirements seem to be complied with, and every nut and bolt was supplied as detailed on the manual. This cost about £150 delivered, fits very well and, as stated previously, needs no bumper cuts. With the towball detached, it is impossible to tell that there is a towbar fitted to the car. If I can fault it at all, the instructions rely a little too much on pictures, and removal of the bumper was not very well explained - yes, the scews were shown, but no further information about the clips etc holding it in place were provided, and I found the disconnection along the sides a little worrying for fear of something breaking!

[Bill Badger]

I'm answering my own questions now, since no one out there could offer a solution, and the connection for Multiplex 1 or Multiplex 2 option was simply down to what the bulb in question is being used for. In my case, the outer rear lights on the 2013 A6 are rear light/brake lights, so Multiplex 1 was the wiring diagram used.

All is working well. The only thing I'd like to change is the supply for the 12V feed to the bypass unit. Due to time restraints (and our current dodgy weather), I have connected the feed to the rear auxiliary socket because I know it is capable of supplying the necessary current. However, as previously stated, this means that the power to the towbar is lost when the ignition is turned off. Can anyone suggest a supply point that would be more suitable, ie one that is sufficient to supply current to the trailer lights in the worst case situation where all could be in use - hazards, rear lights and brakes adds up to about 95 Watts (8 Amps)?

I've fitted a towbar to every car that I've had over the last 20 or so years, and I appreciate that modern electrics combined with a wide variety of lighting options leads to more of a cautious approach. However, I've also learned that out of all car makes that I've owned - Fiat, Ford, Alfa, VW and more, Audi owners seem to be the least 'hands on' and seem to be more inclined to pay the money and have someone else do the work. Not a criticism, just an observation based on the number of forum postings that remain unanswered.

[Dalek63]

thanks for an very interesting thread.

[N22LLO]

Did you fit twin or single electrics?

I'm answering my own questions now, since no one out there could offer a solution, and the connection for Multiplex 1 or Multiplex 2 option was simply down to what the bulb in question is being used for. In my case, the outer rear lights on the 2013 A6 are rear light/brake lights, so Multiplex 1 was the wiring diagram used.

All is working well. The only thing I'd like to change is the supply for the 12V feed to the bypass unit. Due to time restraints (and our current dodgy weather), I have connected the feed to the rear auxiliary socket because I know it is capable of supplying the necessary current. However, as previously stated, this means that the power to the towbar is lost when the ignition is turned off. Can anyone suggest a supply point that would be more suitable, ie one that is sufficient to supply current to the trailer lights in the worst case situation where all could be in use - hazards, rear lights and brakes adds up to about 95 Watts (8 Amps)?

I've fitted a towbar to every car that I've had over the last 20 or so years, and I appreciate that modern electrics combined with a wide variety of lighting options leads to more of a cautious approach. However, I've also learned that out of all car makes that I've owned - Fiat, Ford, Alfa, VW and more, Audi owners seem to be the least 'hands on' and seem to be more inclined to pay the money and have someone else do the work. Not a criticism, just an observation based on the number of forum postings that remain unanswered.

[Bill Badger]

Single electrics fitted.

I bought the detachable towbar from a seller on Ebay. Most seem to be in Nuneaton, but the towbars actually come in directly from Italy. All BS approved and well made. All screws etc provided, as was the 7 pin electrical kit and the all important bypass unit. If you've fitted a bypass kit before, as I had done with a Mondeo, the new one was different. No relays in this one, just electronics and beefy switching transistors! The reason? Because the lights on the car use a pulse system such that the stop/tail light has only a single filament bulb, so the bypass kit has to determine the pulse rate and switch on the appropriate bulb on the trailer. When I ordered my kit, I was asked for the registration number of the car, and I think they can trace this through the system to determine what lights are fitted to my car. Some, as you are probably aware, have LED lights, and for those the bypass kit may be different.

Fitting the towbar was easy once I'd plucked up the courage to be a little brutal with pulling the bumper out of the side clips. All holes are already on the chassis rails, so no drilling was necessary. There is already a hole behind the bumper for the electrics to exit, so it was just a matter of cutting a slot in the rubber bung fitted. The huge alloy crossmember is discarded and replaced with the towbar unit, and I needed to use sealant around the plates covering the entrance to the chassis rails. A little filing of the plates was necessary to match up with the 'L' shape of the steel section added, but it was very minor. No cutting of the bumper was necessary in any way, since it is already moulded as if to be used with a towbar.

The towball attaches easily and can be locked in place against theft. When removed, there is no sign that a towbar is even fitted. I can choose to leave the towball fitted if I wish, but with the huge boot on the A6 I know my ankles will become bruised.....!

Wiring in the electrics took a little thought, mainly because Audi make the trims to fit really well. Getting to the wiring for the tail lights (and brake light - same wire) and the indicators was easy enough. However, gaining access to the fog light wiring was left for another day since unless you know the wire colours it means removing the trim from the boot lid, and I didn't fancy doing that.......
At the moment, the 12V feed to the bypass unit is from the fuse feeding the auxilliary socket in the boot. This threw me somewhat though, because unlike our old Golf, the auxilliary sockets are live only with the ignition on - as I found out one day when trying to charge my phone. I've fed the unit from this though for now just to give me a little protection and to instill a little trust in the bypass unit, although I may wire it via a fuse into the battery. All it means at the moment is that the trailer lights only work when the ignition is on.

I nearly bought a secondhand Audi towbar, but I'm glad I didn't since the coding has to be changed which would add to the cost, and since the car is still under warranty, I didn't feel like having coding done locally by a non-authorised person.

I've just seen the post on how to make the auxiliary sockets permanently powered, so I might do that. Otherwise, as stated above, my lights are ok but the trailer lights go off when I turn the ignition off.

[Atthephoenix]

I have finally completed my 13 pin wiring on my 2013 a6 3.0 avant quattto . Thanks to Bill Badger for steering me in the right direction. I used some break out leads I made , multimeter and a towbar wiring tester I bought off eBay together with some technical knowledge from Steve Smith at Pico automotive technology to understand canbus a bit more than I did and with some perseverance I got it all wired up in the end without using an expensive audi specific harness . I too used a 7 way can bus relay which only cost £20 ok ebay and a 13 pin socket for another £20 ..out of interest the towbar was a BRINK detachable one from Hedleys towbars on ebay and only cosy £169 free delivery . So all in all the whole thing has cost £209 compared with £689 witter wanted to supply and fit !. I've been fitting my own bars since the days off the cavalier and can honestly say that with time , patience and the correct tools the audi was ok to fit . I will add later to this thread the colour coding for the Audi wiring to tap into as for all my research I couldn't find it anywhere on the Web ..
What I can say now is that :
2 feeds come from the outer off side cluster
2 feeds come from the outer near side cluster
And the rest came from breaking into the right wiring loom that runs to the inner clusters via the right hand hinge on the tailgate
AUDI COLOUR CODING AS FOLLOWS :
NS LEFT INDICATOR -BLACK & YELLOW TRACE
BRAKE LIGHTS - GREY & WHITE TRACE
NS LEFT SIDELIGHT - BLACK & WHITE TRACE
FOG LIGHTS - GREY & YELLOW TRACE
OS RIGHT INDICATOR - BLACK & GREEN TRACE
OS RIGHT SIDELIGHT - GREY
REVERSE LIGHTS - BLACK & BLUE TRACE

Dan

[N22LLO]

Any nay luck with your pictures, just picked up a second hand westfalia detachable bar, can't decide now though if to use specific loom so I get the benefits of esc system or whether to just get bypass relay kit.

I have finally completed my 13 pin wiring on my 2013 a6 3.0 avant quattto . Thanks to Bill Badger for steering me in the right direction. I used some break out leads I made , multimeter and a towbar wiring tester I bought off eBay together with some technical knowledge from Steve Smith at Pico automotive technology to understand canbus a bit more than I did and with some perseverance I got it all wired up in the end without using an expensive audi specific harness . I too used a 7 way can bus relay which only cost £20 ok ebay and a 13 pin socket for another £20 ..out of interest the towbar was a BRINK detachable one from Hedleys towbars on ebay and only cosy £169 free delivery . So all in all the whole thing has cost £209 compared with £689 witter wanted to supply and fit !. I've been fitting my own bars since the days off the cavalier and can honestly say that with time , patience and the correct tools the audi was ok to fit . I will add later to this thread the colour coding for the Audi wiring to tap into as for all my research I couldn't find it anywhere on the Web ..
What I can say now is that :
2 feeds come from the outer off side cluster
2 feeds come from the outer near side cluster
And the rest came from breaking into the right wiring loom that runs to the inner clusters via the right hand hinge on the tailgate
AUDI COLOUR CODING AS FOLLOWS :
NS LEFT INDICATOR -BLACK & YELLOW TRACE
BRAKE LIGHTS - GREY & WHITE TRACE
NS LEFT SIDELIGHT - BLACK & WHITE TRACE
FOG LIGHTS - GREY & YELLOW TRACE
OS RIGHT INDICATOR - BLACK & GREEN TRACE
OS RIGHT SIDELIGHT - GREY
REVERSE LIGHTS - BLACK & BLUE TRACE

Dan