[CurtCharlesPDX]

I think I'm all ready to set up my 2012 VR6 for towing.

I have a VW 7P0803881 hitch. There are many YouTube videos that show how to install it. I'm not concerned.

I have the VW 7P1055203 trailer wiring package with 7-pin connector. The package wants me to apply a sticker that reads "no brake controller". Is this package compatible with a brake controller?

The instructions that came with the wiring package indicate that the dealer needs to make computer adjustments so that the car recognizes the electronics. I've not seen anyone here mention that...

I understand that I'll have to search for the brake controller connector under the dash, and that I'll have to build a little harness from the VW connector to the Tekonsha P3 connector. No problem, I will have the mate to the VW connector on Monday.

Finally, I've seen multiple posts that I may need to do some custom wiring from the brake light switch through a relay to the Teknosha P3 connector. But not all installations of a Tekonsha P3 on a Touareg say so. Advice please?

 

[ToolmanJohn]

Yes, the dealer will have to code the Touareg because it's not factory installed.

Yes, that little harness requires buying 3 items. The plastic "molex" style connector, and two pieces of wire that have the connector "molex" tabs already crimped on. Those wires get cut in half and you have 4 wires with crimped on connectors to make the adapter for the brake controller. I thought it was kooky that I had to do this, but it wasn't difficult except for getting the parts. I had to go to an Audi dealer that had them in stock, it was cheap.

Yes, the brake controller is tucked up inside the left side of the dash possibly near the A-Pillar. Not possible to see, but by hand you can get it.

You may, or may not, need to install an auxiliary relay to deal with flickering or non-functional brake lights. Tekonsha recommends using it from what I recall. It really depends on the Touareg and the trailer brake lights. For some people the Tekonsha P3 works fine (I have one, and LED trailer brakes lights, and no problems). For others, the small square wave voltage that checks for burnt filaments causes problems with activation of the trailer lights when using the Tekonsha. Test first, then if needed, follow all the instructions in the posts if needed to make that auxiliary relay dongle.

http://www.tekonsha.com/support/installation/N90195.pdf heres a link to operation instructions.

Also, https://www.etrailer.com/faq-tb-09-0021-Tekonsha.aspx wiring diagram for the breake relay courtesy of eTrailer, a great resource.

There are some great threads that explain all this. Also this is covered in a Cayenne forum IIRC.

 

[CurtCharlesPDX]

Well, I spent 30 minutes with my head under the dash and I'll be darned if I can find that connector. I've heard it's "way up there" and "near the A piller", so that's where I looked. I folowed several loom branches, but none seemed to end in the alleged foam-wrapped connector. This seems to be a rather important element of the installation and I'm lost...

 

[ToolmanJohn]

It's there. I had to reach nearly my entire arm up into the dash, and it was somewhat on top of a ledge near the A-Pillar. The technicians that install the dash console probably tuck it away differently every time. I didn't have to follow any wire looms, I just had to spend a lot of time feeling for the foam covered connector. Once I had it, it only pulled down another 10-14 inches, and wasn't even flush with the bottom of the dash, it took a bit of effort to connect the new brake controller adapter into it one handed.

 

[CurtCharlesPDX]

Thanks. I'll give my back a rest tonight, and try again on Wednesday. I will also remove the fuse block panel to see if that gives me better visibility.
Can you confirm that getting the solid 12V and ground for the relay from the VW connector is acceptable? Also, is there a pin-out on the VW connector, or do I need to determine the wire colors to know which signal is on which pin?

 

[ToolmanJohn]

Thanks. I'll give my back a rest tonight, and try again on Wednesday. I will also remove the fuse block panel to see if that gives me better visibility.
Can you confirm that getting the solid 12V and ground for the relay from the VW connector is acceptable? Also, is there a pin-out on the VW connector, or do I need to determine the wire colors to know which signal is on which pin?

I'll try and find that wire diagram. I did mine in 2013.

Found one with the relay option.

https://www.etrailer.com/static/images/pics/q/u/qu39088_2_800.jpg

And another which shows the wiring diagram even better. As I said before, I did NOT use the auxiliary relay. My Tekonsha P3 works fine with my trailer.


https://www.etrailer.com/faq-tb-09-0021-Tekonsha.aspx

 

[CurtCharlesPDX]

Thanks Toolman John. I spent 90 minutes on my back underneath the dash. I removed 3 panels to get better access, and at long last I laid fingers and eyes on something hard wrapped in gray foam.. But, I was unable to move it more than 1/4" in any direction, and I couldn't fold back the foam. I've seen pictures of it near the fuse panel on the left of the "concertina" structure, which implies a few inches of slack in the wires.

It reads like you left it on the little shelf. That may be the best choice, and I could possibly do the same, but at this point I haven't seen the actual connector housing.

I think I'll see if the local shop will expose it for me; I don't think I'm capable. I hate giving up.

 

[CurtCharlesPDX]

Partial success

I installed the electronics in the back; very straightforward after opening the back right panel, which isn't quite so simple. The OEM kit fits perfectly, and the red connector, unlike the one for the brake controller, is right where it needs to be. And there is even enough slack, so that it reaches.

We successfully removed the bumper cover and the bar. Then we discovered that the factory hitch requires longer bolts which weren't supplied with 790803881. Does anyone know where to get the right bolts? Can I go to Fastenal and get M12x85mm SST bolts with a washer?

I've built the harness for the brake controller and included a 30A self-resetting fuse on the 12V line from the vehicle. I'll verity that the right things are on the right pins before connecting the P3. If I have the wrong things in vehicle-side plug, does anyone have advice on how to remove the pins from the housing?

Next week I'll pay to have the connector under the dash exposed; I gave it 2.5 hrs with no success.

 

[HookedonV10s]

Make sure you run the power and the ground for that controller to the battery. It is not that hard to access the cables in front of the drivers seat.

 

[FSJ Guy]

Might want to consider buying VCDS. It will let you re-code for your trailer module and much more. $$$, but worth it.

The dealer will likely want at least 1/3 of the price (if not more) of VCDS to reprogram the module.

 

[Spiegelglatt]

Only factory bolts. Get the right ones, they have a specific strength rating (that is very high). Early 2003-2004 Treg's had bad factory bolts (for example) that had issues bending and nearly failing. Better safe than sorry and get the right stuff.

I would still do this even if you don't plan to tow big, because later you might and forget the bolts are not up to the job.

 

[CurtCharlesPDX]

The factory non-hitch bolts are an M12-1.5 flange bolt with a 18mm head. Standard thread for an M12 is 1.75, and neither of my socket sets don't included the 18mm.

For the hitch, I need an additional 37mm of bolt length past the 45mm on the stock bolts. 90mm should work, but maybe 100mm.

McMaster has M12-1.5mm 90mm Class 8.8 McMaster-Carr ($11.79/5)
Fastenal has M12-1.5mm 90mm Class 10.9 https://www.fastenal.com/products/de...M12-1.5+x+90mm ($4.74/1)

From my calculations, the Class 8.8 will work just fine. They are rated at 115,000 PSI so each can hold 20,000 lbs in tension, and were the Treg suspended from the bumper that would only be about 625 lbs per bolt. So it seems like even at the soft Class 8.8 there is plenty of overkill. Tension forces should be limited to acceleration and slope; accelerating a 7700 lb boat up a 30 degree boat ramp should max out the tension on the bumper at about 4000 lbs. Divide that by 8 for 500 lbs tension on each bolt, giving a 40x safety margin. There's less than 100 lbs in sheer on each, so sheer is well under the limit too. If you really don't like the idea of a Class 8.8 (US class 5 equivalent), then the Fastenal bolt is an option giving Class 10.9 (US class 8 ).

8 bolts on the hitch is crazy overkill. I like that.

Torque the 8.8 to 69 ft lbs for maximum strength.

 

[noobytoogy]

Excellent post I don't fully understand except that the bolts will do the job required of them!

 

[gnrnr]

The factory non-hitch bolts are an M12-1.5 flange bolt with a 18mm head. Standard thread for an M12 is 1.75, and neither of my socket sets don't included the 18mm.

For the hitch, I need an additional 37mm of bolt length past the 45mm on the stock bolts. 90mm should work, but maybe 100mm.

McMaster has M12-1.5mm 90mm Class 8.8 McMaster-Carr ($11.79/5)
Fastenal has M12-1.5mm 90mm Class 10.9 https://www.fastenal.com/products/de...M12-1.5+x+90mm ($4.74/1)

From my calculations, the Class 8.8 will work just fine. They are rated at 115,000 PSI so each can hold 20,000 lbs in tension, and were the Treg suspended from the bumper that would only be about 625 lbs per bolt. So it seems like even at the soft Class 8.8 there is plenty of overkill. Tension forces should be limited to acceleration and slope; accelerating a 7700 lb boat up a 30 degree boat ramp should max out the tension on the bumper at about 4000 lbs. Divide that by 8 for 500 lbs tension on each bolt, giving a 40x safety margin. There's less than 100 lbs in sheer on each, so sheer is well under the limit too. If you really don't like the idea of a Class 8.8 (US class 5 equivalent), then the Fastenal bolt is an option giving Class 10.9 (US class 8 ).

8 bolts on the hitch is crazy overkill. I like that.

Torque the 8.8 to 69 ft lbs for maximum strength.

What is the shear strength on the bolts? or are they actually loaded in tension? I've not had a look at how the bolts work on the towbar for the touareg, hence my question about the loading direction.

 

[alnl1996]

All you need is 3 things to get that brake controller plug out of your dash.
A flashlight
A coat hanger
And a shot of Vodka
That's it.

 

[CurtCharlesPDX]

Outstanding. I was considering having a u-joint installed between my elbow and my wrist...

In installed the hitch this weekend. Very easy, but way too many fragile plastic clips on the wheel-well trim pieces. Also, a little tricky to get the bottom of the bumper cover over the safety chain rings, but not impossible. Looks great fully installed.

I checked the 7-pin too. Right turn, left turn and running lights work fine. Didn't check brake lights or battery charge. So far, it's looking good!

Without stopping the engine I disconnected and pulled away. Much to my delight I saw messages "Trailer brake lights not working" and "trailer right right out". I didn't expect that!

 

[CurtCharlesPDX]

12,814 lbs force in sheer.

 

[CurtCharlesPDX]

SUCCESS! I finally located the ellusive connector, and I found it on my 2012 exactly where folks said it would be. However, even with really long arms I was unable to extract it. Desperate times call for desparate measures. In my case, I first removed the fuse block. The I located 4 bolts (10mm hex heads with a T30 inside) that restrain the black plastic electronics interconnect boxes. This allowed immediate and easy access to the brake controller connector, visible above a black connector with a purple lock.

The only surprise is that the Tekonsha P3 appears to be powered even with the engine off, which seems like a bad idea.

Here's my schematic for the wire harness I built. I won't know if it really works until I connect the trailer.

 

[Ewie]

Curt....
The schematic is exactly the same as the harness I made for my P3, except I included a switch on the earth wire to the relay (have never used the switch so would probably leave it out if repeating the exercise). A big thanks to those early posts that pioneered this solution.


This set up has worked perfectly for me and I can see no reason that you should not see the same results.

 

[CurtCharlesPDX]

I did a short test run, and the P3 controller works great! Stopping is well controlled and I feel very confident.

However, one serious problem. No trailer brake lights. Right turn, left turn work fine. Running lights are fine. 4-way flashers are fine. But no trailer brake lights.

I get a "left trailer light out" warning on about 50% of the engine starts when connected.

Yes, I used the factory harness and 7-way connector.
No, I don't have the car coded for towing yet.

Suggestions?