Installing a hitch & wiring on a 2004 S4 Avant

To begin with, I will flame myself to save everyone else the bother. It is a sacrilege to put a hitch on an S4. I should buy a pickup or SUV if I need to haul things. S4’s are made for a different type of hauling. Etcetera, etcetera, etcetera.

Now for the reason I am posting. I found very little information on installing the hitch or wiring on a B6 S4. Hopefully, the words below will help. I have posted photos as well at:[email protected]/sets/

I have installed a number of hitches on cars over the years as I have never owned a pickup and only a couple SUV’s. I enjoy driving a sporty car which can be used for utility purposes when necessary. This is one of the easiest hitch installs I have done. I bought the hitch from and it was packaged very well. The hitch is made by Curt Manufacturing and I have used their hitches on other cars and have always been pleased with the fit and finish. Directions and a draw bar come with the hitch. You will have to buy your ball and a wiring adapter.

Installing the hitch:

1. Remove the spare tire.
2. There is a tow hook attached to the bottom of the spare tire well. Place the hitch just above the tow hook and center it so both sides of the hitch are flush with the side of the spare tire well.
3. There is a bracket used to attach the hitch to the tow hook. Install the bracket and snug it up.
4. Once you have it snugged in place, drill the four holes to mount the hitch to the spare tire well. The instructions say to mark the places to drill and remove the hitch for drilling. Once I snugged the hitch in place, I drilled the holes with the hitch in place. You wll need a right angle drill with a short drill bit as there is not much room on either side.
5. Once you have the holes drilled, install the bolts. I made a mistake here and installed the bolts from the outside of the car when I should have installed them from the inside. I had to cut off the bolts in order for the spare tire to fit in the well. I did place a rubber seal on the inside to help prevent any water leaks.
6. Tighten up the bolts and you are done.

The more difficult part was installing the wiring harness. You will need to purchase a wiring adapter that converts five wires to four. I bought mine at Advance Auto Parts but they are available at most places that sell trailer wiring harnesses. You will see a photo of the adapter at the photo site.

Installing the wiring:

1. To get the tailights off the car, you need to pry off the small plug on the side panel. It is located on the trim piece about 10″ up from the floor on either side. Once you have pried it out, you can insert a Phillips screwdriver to unscrew the bolt that holds the tailights in place. Once you have loosened that bolt, push out on the tailights to break them loose from the car. It will take a determined push.
2. Once you have the tailights hanging from the rear of the car, you can find the wires that you need to tap into. All but one of the wires you will be tapping into are on the left side.
Gray wire-running lights
Blue/Green wire-Left turn signal
Red/yellow wire-brake
Ground wire-Brown
3. On the right tailight you will find the one wire needed there
Yellow wire-right turn signal
4. Remove both side access panels
5. The left tailight wires run behind the black box on the left side. To access those wires, you will need pull out the left side trim panel far enough to remove that black box. Remove both tie downs and the screw at the rear upper corner of the side trim panel. Pull out on the panel on the side at the rear. It has two metal clips that go into metal holes on the side. It also takes a determind pull but be careful that you do not crack the panel. Once you have it released at the rear, you call pull it out far enough to access the two bolts and one nut that are holding the black box in. You do not need to unhook any wiring from the back of the box. Once you have all the bolts and nuts removed from the black box, you can finagle it through the hole in the side panel.
6. Once you have the box out, you will see the wires running along the side of the car. This is where I tapped into the wires for the adapter. I soldered my connections but you could use clip on connectors. Remember that these connections will be hidden once you are finished are not easily accessible. If you know how to solder, I would take the time to do that.
7. On the right side, also remove the tie downs, the top screw in the corner and pull out the panel from the side of the car. Here, I did not remove any items that are directly behind the access panel. Once I pulled out the side panel, I could reach the wiring for the right tailight where it came through the body. However, I did not have room to tap into the wires here. Since I only had one wire to run on this side, I tapped into the wire on the harness from the body of the car to the tailight. I punched a small hole in the rubber grommet and pushed the wire through the grommet from the tailight side. I could then pull the wire through on the inside of the car. I ran the wire along the rear of the car under the rear brushed aluminum trim piece that I had removed. I then attached that wire to the wire for the right turn signal at the adapter.
8. Once you have all the wiring complete, put everything back together and you are done. When re-installing the bolt that fastens the tailights, install the bolt while you have the rear side panel pulled away. It makes it much easier to get to and less chance that you will drop it into the abyss. I ran the wiring harness beneath the side panel into the area above the spare tire. The carpeted rear panel will hide the wire when you do not need it. When pulling your trailer, simple pull the wire out from beneath the carpet panel and out the rear hatch.