400North

There appear to be lots of good posts about installing a Curt trailer hitch, or a trailer brake controller on a Cayenne. This is to summarize what I couldn’t find – guidance on the installation of a 4 pin trailer wiring harness. I’ll never be towing anything large enough to require trailer brakes. The following will work for smaller utility trailers and boat trailers without brakes. As such, I prefer to have the wiring tucked away where it stays clean, next to the spare tire. When I do use a trailer, I open the spare tire door, hang the 4-pin trailer harness out the trunk door and close the door.
After installation I have no error messages on the instrument panel when trailering. Although I don’t have LED lights on my trailers, the Curt literature says this will work with standard or LED trailer lighting systems.
I used the Curt trailer wiring controller module – part number 56146 although I’m sure there are lots of similar, comparable units on the market. It cost roughly $20.
1. Start at the rear with removing the right side access cover. On the left side, the access cover as well as the enclosure with shelf will have to be removed. That black enclosure has 2 torx screws securing it at the top. It can be removed without needing to remove the entire interior panel that the access cover fits into. With the enclosure out, you should now be able to see the factory wiring harness leading up to each rear light.
2. Lift up the access door to the spare tire and remove the floor panel (the one that’s about 3 inches wide) that’s on the left of the access door. It’s held on with 5 screws.
3. I found it works well to end up with the control module positioned under the spare tire door at the left side. It comes with double sided tape to secure it. Just place it in the approximate position for now. You’ll tape it in place once all other steps are complete.
4. The white ground wire from the control module comes with a xxxxx fitting. Feed the wire alongside the existing Cayenne wiring harness to connect with the Cayenne ground terminal that sits inside the left access area under the taillight wiring. The Curt module has the ground wire length and fitting size for you to connect the ground now.
5. Carefully cut open the Cayenne wiring harness about 6 inches from the point where it disappears to connect with the taillights. Do both sides. Using scissors are a good idea to help avoid nicking any wire insulation. You’ll want to expose about 3 to 4 inches of wiring in order to make your connections.
6. Take the long green wire coming out of the trailer controller and route it alongside the Cayenne wiring harness to the place where you’ve exposed the wiring near the right side taillight. Use the supplied wiring connector in order to connect the green trailer controller wire to the black with green stripe right turn wire of the taillight wiring harness.
6. There are 3 wires leading out of the trailer controller that you’ll want to now feed the same way as the ground wire. Once fed through to the left side wiring that is now exposed, you’ll want to use the supplied wiring connector to connect as follows…

Curt trailer controller wiring to factory taillight harness wiring:
- Yellow left turn wire to black with white stripe wire
- Brown running light wire to gray with black stripe wire
- Red stop light wire to black with red stripe wire

7. Now you are ready to connect the trailer controller 12V power wire to the Cayenne battery. For this you’ll need to have purchased (from any auto parts place):
- a roll of 12 gauge electrical wire
- a 12V fuse receptacle
- a 12 gauge ring terminal similar to the one on the controller ground wire. Look for one sized for a #10 stud and the weather-resistant variety that comes with shrink-wrap fitting if possible.
Open the driver’s side rear seat door. I found that I could feed the 12 gauge wire up from the point where the 2 pieces of carpet meet near the back side of the seat bottom, right beside the door opening. The 12 gauge wire is reasonably stiff and I could feed 3 or 4 feet up inside the left rear fender cavity. Then going to the back and reaching in through the left side fender cavity opening, I could reach the wire and pull it back to where I’d just made the other connections. Feed the wire alongside the factory wiring harness, then alongside the 3 Curt signal wires and the ground wire to the trailer controller module.
Now you’ve got some connections to make to connect your 12 gauge wire to the black Curt controller battery wire. Either use electrical connectors you’ve bought from the same auto parts store, or my preference, soldering and shrink-wrap tubing.
Between the 12 gauge wire and the trailer controller, I’d recommend installing a 12V fuse receptacle. You’ll then have easy access to the fuse, as it will be right alongside the trailer controller. A 10 amp fuse should be sufficient.
Once all electrical connections have been made at the back, pull out the fuse for now. Go to the driver’s side rear door and tuck the wire under the plastic trim piece as you work towards the driver’s seat.
Now it’s time to access the battery. You’ll need a 10mm triple-square socket to remove the 2 bolts at the front of the driver’s seat. The owner’s manual provides guidance here too. Once I tipped up the seat, I was happy to see that the Cayenne has a 12V electrical bus alongside the battery making the next steps easy. Access it by flipping up the black plastic panel that sits right beside the battery panel. There were several terminals on the electrical bus that were unused on my Cayenne. I added a ring terminal connector to my 12 gauge wire and then with a 5mm nut, attached it to one of the available 12V terminals on the electrical bus.
8. Time now to put your trailer controller fuse back in place and test that you’ve got functioning running light, brake light and turn signal functionality.
9. Assuming that all is working, you should now use the nylon zip ties to secure the wiring that feeds the trailer controller to the Cayenne wiring harness. I also used electrical tape to cover over the places where I opened up the Cayenne wiring harness near the taillights. Then reinstall all the access panels in the trunk area. Lastly, use the supplied double sided tape to secure the trailer controller in the spare time cavity.

s4for5

Good documentation
I now know exactly how I will run the power to my boat trailer winch connector
Excellent post timing for me, thanks

Divot

...and Larry's corpse begins to climb up the cliff.

pumper

Nice description. What year/model Cayenne do you have. Will this work for an 2004 CS with navigation?

JFScheck

Why not just use the 7-pin to 4-pin adapter - then if you ever sell your Cayenne you give that option to the next folks (or if you ever need to tow a larger trailer)....

Bonus - you have the electronics module for the lights as well (bonus for 2006 and newer perhaps - 2005 and older make sure you get the bios update)...

ltc

Impossible.
Per his last wishes, he was given a Viking funeral (unfortunately, his not so beloved P!g did not share the same fate that day)...



Helga, shown here, was in charge of the funeral service and can be contacted with further questions...

JONSEACLIFF

Hi 500North.
Thanks for posting the Cayenne wiring instructions. I have ordered the kits from etrailer.com and will follow them to the letter. One question: Do you think it's practical to install a small rechargeable 12v dry cell battery near the controller instead of connecting to the vehicle's battery? I'll only be using the trailer for brief trips during daylight hours and as I live in L.A. I rarely use my turn signals or brakes. :-)
Best regards.

JONSEACLIFF

I went ahead and installed the unit as described on my 2008 GTS. I didn't receive an answer to my question about using an extra battery so I attached the power wire to the vehicle battery as described above. I did everything methodically, and after installation, the trailer lights all worked correctly and I thought I'd completed a trouble free project.
HOWEVER, soon after I disconnected the trailer, error messages started to appear on the dash display. "CHASSIS MALFUNCTION", "BRAKE PROPORTIONING MALFUNCTION" etc. At one point the vehicle even locked itself in Park. However, after a couple of hours it sorted itself out and reverted to normal operation, except that the "Check engine" light was on. This also disappeared later. Next day error messages appeared again only to disappear again after being parked for a while.
I called Curt, but although they were sympathetic, could offer no help (except a refund).
I tried pulling the fuse from the power wire to the Curt controller, and everything is now fine and was completely normal over the weekend and this morning. Of course I'm now concerned about warranty issues, my second service is due soon. It seems that the Cayenne's computer can detect when its battery is connected to a unit it doesn't recognize. I think I'll try my original idea of a small auxiliary battery and see what happens.
Any other ideas?

cbracerx

Subscribed.

wirunner

I was waiting for this post. How dare you try to use a non-OEM towing control unit (and save money)...

ltc

I don't think so.

400North

I don't understand why you'd be getting messages such as brake proportioning malfunction if you've only installed a 4-pin trailer wiring unit. With that, you need no brake controller unit, and you're not dealing with trailer brakes. I'd suggest you might want to try connecting to another trailer and see if the errors disappear. If so, you've got a problem in your trailer's wiring. When not trailering, I would definitely recommend using one of those rubber covers that go over the 4-pin connector. If you have that 4-pin connector bouncing around next to your space tire with the pins exposed, I'll bet there's a good chance of getting intermittent shorts

JONSEACLIFF

I installed a 12v, 12.5ah sealed battery that fits snugly in bottom of the left rear storage area and connected it to the controller.
All the trailer lights work correctly and there were no error messages during or after the trailer was connected.
I used the in-line fuse as before and quick connectors so that the battery can be removed easily for recharging.
I believe this setup is OK for light duty use and it saves the hassle of wiring through to the vehicle battery.
Plus the entire system can be removed in a few minutes if desired.

ltc

Something doesnt' sound quite right with this...

Aremee

I tried following the instructions, and nothing about taking the panels apart seemed to be accurate. Couldn't find any access panel to the left of the spare tire compartment, not sure if I needed to remove the OEM Bose sub woofer that is underneath the tire. On the left side of the car, which I figured was the passenger side, it wasn't identified, I have a CD Changer, again, OEM, and the shelf that is described is impossible to get out as described when there is a CD changer. I am just wondering if the wiring described in this post is even accurate before I start trying to wire my hitch. Any comments would be appreciated.