T5 Multivan trailer wiring

[pjondeck]

I decided that I was sick of messing around with the adaptor lead for the trailer. Having identified backwards from the trailer the seven wires on the seven pin side of the 12 pin plug to the 13 pin round VW socket and thence in the main loom, I proceeded to make the same connections from the loom to the flat socket. I replaced the changeover switch embedded in the VW socket with a changeover switch mounted beside the socket on the vehicle. At first when I flashed it all up I got some weird goings on on the trailer lights so I took the car for a short drive with nothing connected and then tried it again. I now have tail/side lights, right hand indicator but no brake or left hand indicator. I have checked my wiring and have checked for voltage output on the actual loom but zilch. Could it be that I might have to have my ECU reset?
Any suggestions appreciated.
Many thanks
Peter

[Sunny43.5]

Maybe disconnect the battery and try again it will reset if something has gone wrong . PS we have done the same thing have gone to the big plug but we ran our wiring for the trailer via an adaptor kit . It negated the need for having to get VW to turn it on and we are running full LED lighting as well .

[Umai Naa!!]

The adaptor has diodes in it to work with the bulb monitoring. The trailer control module has factored all this in, but is now seeing difference resistance readings, from not having the adaptor harness in place.

The best solution is to fit the adaptor harness permanently behind the bumper, with only the 7-pin plug showing. Make sure you tape it all up to minimise water ingress.

Also, don't test these with an LED circuit tester/test light. You need to use an old school incandescent one.

[pjondeck]

Thanks for the info Sunny and Amai. I'm wondering if the idea of leaving the adaptor cable in circuit may have been the easy way out but try to keep the connections to a minimum so went this way. It would be a bit of work to go backwards now but will keep that as an option.
I have been running LED's on both of my trailers and these days with more leds in the units I haven't had a problem with lack of current drain. Is the consensus that I might have to get VW to enable the system then?
ta again

[Umai Naa!!]

There is another adaptor harness available from VW that will function with LED lights on your trailer.

[pjondeck]

Does the adaptor harness eliminate the big VW plug? Is it something that shows the colour code connections from the original loom? I will try the battery disconnect this morning and also look for a blown fuse just in case but the adaptor harness may be an option. Do you have any info about the other harness you mentioned please Umai?
cheers and thanks again

[Umai Naa!!]

LED-friendly adaptor plugs into the 13-pin plug.

[pjondeck]

Thank again Umai
I have included the diodes that existed in the adaptor cable in my connections. They do however only seem to isolate the left and right tail/running light feeds that are split in the main vehicle form so that they can be combined on pin 7 (tail light) of the 7 pin socket.
If I installed the adaptor cable permanently (bit late now methinks) then the micro-switch therein will be telling the vehicle that there is a trailer permanently connected. I have checked, rechecked and rechecked again my wiring and am confident that there is no electrical difference to what was there using the adaptor cable. If I plug the trailer in on one occasion I will have tail and RHS indicator working normally only. The next time I plug it in I get tail and Left indicator pulsing ten to the dozen and they continue to do this for about ten seconds after I have turned off the vehicle and pulled out the key! I am waiting for a call from the dealer who installed it to find out exactly what is in there. I'm wondering if I should just go to a dealer and ask them to put it on the analyser and see what we see? The changing effect makes me think the system might need resetting. Will see what happens there but may want to ask you more about the adaptor unit you mentioned.
Thanks again

[Peter Jones]

OK we just need to clear up a bit of misinformation here.

Firstly the micro switch has nothing to do with trailer detection.

Trailer detection is done by the trailer detection unit looking for the globes on the trailer.

The pulsing you're seeing in the LED lights is the way the system checks the globes.

The micro switch disconnects the vehicle fog lights when the trailer is plugged in and connects the circuit through to the trailer.

The adapter that VW sells is just a box full of resistors that provide the same load as normal incandescent globes. You may still get the flashing effect with it installed. It will probably stop the globe out warning light though.

As to the diodes in the adapter plug - they're unnecessary if the car is coded correctly.

The trailer module in the car should be coded to Australia. When coded this way only the left hand park light circuit is active. You use this to feed both left and right on the trailer.

If it's coded to "rest of world" both left and right park circuits are active.


There's heaps of threads on this on the AusAarok forum. The Amaroks share a lot of electronics with the transporters.

This is a chart I made up on changing the Amarok 13 pin plug to other plug types

Function	13 Pin Plug	Colour	7 pin plug	12 Pin plug
Left Turn	1	violet/red 1.0mm	1	1
Rear Fog Light	2	grey/blue 1.0mm		11*
Earth	3	brown 2.5mm	3	3
Right Turn	4	violet/grey 1.0mm	4	4
Right Parker	5	grey/blue 1.0mm
Brake Lights	6	black/red 1.0mm	6	6
Left Parkers	7	grey/yellow 1.0mm	7	7
Reverse	8	black/blue 1.0mm	2	2
Battery 12v	9	black/red 2.5mm		8
	10
	11
	12
Earth	13	brown 2.5mm		10
Trailer Brakes			5	5

I included the 12 pin flat plug too. * Some of these have a micro switch in them too so you can wire in the fog lights like VW did.

You can plug a 7 pin trailer plug into a 12 pin socket so they can be used for 7 or 12 pin equipped trailers.

This is all assuming the car is correctly coded for Australia.


Sadly there's no easy way to make the OEM system wok reliably with LED lights. Sometimes you get lucky and there's no issues other times they'll drive you mad.

The best solution at the moment seems to be swapping out the OEM trailer detection unit for an after market one from Milford.

I took an easier path though and wired my trailer to euro spec including the 13 pin plug, incandescent globes and seperate left and right park circuits. Works perfectly.

[Stuart Martin]

This is a chart I made up on changing the Amarok 13 pin plug to other plug types

Function	13 Pin Plug	Colour	7 pin plug	12 Pin plug
Left Turn	1	violet/red 1.0mm	1	1
Rear Fog Light	2	grey/blue 1.0mm		11*
Earth	3	brown 2.5mm	3	3
Right Turn	4	violet/grey 1.0mm	4	4
Right Parker	5	grey/blue 1.0mm
Brake Lights	6	black/red 1.0mm	6	6
Left Parkers	7	grey/yellow 1.0mm	7	7
Reverse	8	black/blue 1.0mm	2	2
Battery 12v	9	black/red 2.5mm		8
	10
	11
	12
Earth	13	brown 2.5mm		10
Trailer Brakes			5	5

I included the 12 pin flat plug too. * Some of these have a micro switch in them too so you can wire in the fog lights like VW did.

Thanks Peter, this is exactly what I was looking for. My wire colours are slightly different but I was able to work it out. I wanted to go directly from the wiring loom to a 12 pin trailer socket to reduce the number of connections and the original 13 pin socket was badly corroded with screws broken, wires soldered in and unrepairable.
I followed your table and it worked first time. I do get a bulb out warning light on my dash when the trailer is connected with the lights on, but I am not worried about that. I have a load box but not interested in wiring it in.
Cheers.