Originally Posted by malibu111

Call it a hack job if you like but here's the simple installation if you don't have the camera and safety backup indicator. After a lengthy investigation, this was my working end solution.
1. Purchased Curt hitch, $156.00 to the door and installation.
Remove back bumper screws, both underneath tail section and under wheel wells. Make sure you find all (5) on each side by tire. Make sure you find the one hidden behind the felt wheel well liner. Prepare to pull hard to get the side end-points off.
2. Purchased the Curt C56200, $80.00 wiring harness. You need to PWM type because the brake and running lights operate from a single wire connection.
The key here is to identify the signal wires from the tail gate light assembly NOT the electronics bay. I did tap into electronics bay for ground in the rear right side and found a constant hot wire on the 12 cigarette adapter at the rear and inline fuse at this point. The Q7 has separate light assemblies which operate active/passive. When tail gate is open, lower bumper lights are active and when hitch closed, tail gate lights operate and bumper go passive state. You must probe for blinker and running/brake lights on the tail gate assembly with the door closed. Yes, you need to get in the back with the gate closed and probe like I did. I purchased a $6.00 12volt probe tester from Harbor Freight, love that place.
Driver side tail light connector, pin BLUE- RED stripe (L-Blinker). I tapped this wire and ran across tail gate and down into electronic bay to C56200 module.
Passenger side tail light connector, same as other side, pin BLUE- RED stripe (R-Blinker). I tapped this wire and ran extension wire down to the electronic bay to the C56200 module.
Stop and Running lights provide (2) hot wires on each side in the tail light section. You can tap any one of the four wires as they all operate the Stop running lights. Why you ask, because there are two main tail light BULBS on each side. I tapped into the one on the passenger side as this is closer to the electronic bay. Neatly route the wires alongside the factory wire harness.
Ok, I now have three wires to dress down from the tail gate into the electronic bay and attach to the standard trailer wires, Green/Yellow and Red. Follow the color codes in the harness directions.
The tail gate cover can be challenging but here’s my method.
1. Remove the small plastic strip at eye level at the top roof line first.
2. Remove the two upper side plastic strips close to the roof line next; they overlap one another at the edges.
3. Remove the large tail gate cover
a. Disconnect the small interior light assembly, pops out by rocking socket…use caution…gentle
b. Remove tailgate button in the same manner as above
c. Remove screws in tailgate and there is one in each tail light section
d. Pull and detach heavy interior cover plate
e. Tap into necessary wires, use type wraps and do a clean job
f. Put all panel back on after testing
4. Testing and flat 4 ping connector goes as follows
a. With my probe, I attached to body ground and probed the 3 female leads in the plug
b. L - blinker should flash on one pin only
c. R - blinker should flash on one pin only
d. Stop - blinker should flash on all pins
e. Flashers and running lights on, all flash and blink on respective side
I never had to address the front of the vehicle. The only activity in the rear electronics bay was a self-tapping screw for ground and borrow the cig-lighter constant hot lead.
My 4 flat pin is now in the rear tray and I plan to drop it out the tail gate when needed. You can route the harness out the one and only rear rubber grommet which is literally buried in the back right corner behind electronics.
If you want to go all-out and require power brakes and have the camera and backup sensor systems, you need to get your wallet out and purchased the control module which would installed in the electronic bay. The right rear bay on these vehicles is full of harnesses and various module and for your spending pleasure. The fully loaded Q7’s need to provide feedback to the computer system that I have a tow behind me and disable camera and backup sensor system. In addition, the vehicle adjusts suspension and puts you in tow mode. Basically, you are telling the vehicle to adjust as soon as you attach the harness.
The OEM hitch is a NO brainer, double the price for Curt, which is nice by the way…pretty damn heavy. The only advantage to the OEM towing harness is the exterior receptacle is attached to the hitch and the harness is dressed through the side rubber grommet and then snakes into the electronics bay and attached to the control module. Simply attach tow trailer wire and a feedback signal talks to the vehicle and sets up the suspension and disables the necessary caution systems.
The only drawback is that the OEM system out of the factory is very expensive.
I wouldn’t be surprised if you could disable these nice features when towing by removing the fuses that run them and go the cheaper route like I did. All said and done, I spent $240.00 for my attachment.