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Tekonsha Trailer Wiring Harness Installation - 2014 Audi Q5

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How to Install the Tekonsha Trailer Wiring Harness on a 2014 Audi Q5

Today, we're going to be taking a look at the Tekonsha upgraded ModuLite trailer wiring kit, along with the Buyers trailer adapter on our 2014 Audi Q5. Now our Tekonsha wiring is going to provide us with the 4-way trailer connector. However, a lot of people have trailers that have a 7-way on them. And that's where our Buyers adapter going to come into play. The adapter is going to give us a 7-way. So we'll have all seven functions like our tail lights, brakes, turn signals, reverse lights, and we even have the option to put in a brake controller and have a 12 volt power source.But the nice thing is, is we still get that 4-way on the outside as well.

So we'll have a dual connector here. That way if we have two different trailers, different connectors on there, or if we just tow several different trailers, we'll be able to hook up really easily. Now I do want to mention that this is a pretty common thing. People want to be able to use a 7-way on their Audi. However, the Tekonsha wiring is meant to stay on the inside of the vehicle.

So the problem comes up to get that wiring outside, so that we can mount up the 7-way.But our Tekonsha wiring is going to be stored on the inside. The converter box and everything else is actually right behind this panel here. We just pull that panel out of the way. We can see we have our converter box and all of our signal wires hooked up. Now the converter box is going to take the signals from our factory wiring, and convert them into a working signal for our trailer.

It's also going to make sure that there's no feeding, and it's going to protect our factory wiring from any kind of potential issues that may be on the trailer end.Another thing I really like about the Tekonsha ModuLite here is that it is fuse protected. So we don't have to worry about overloading our taillight circuits or turn signal circuits from our trailer wiring, because it's going to have its own power source, that we're going to have to hook directly to the battery. And our Tekonsha wiring is going to plug directly into the back of our Buyers adapter so that way we're not going to have to worry about cutting or splicing anything on that end.That way we get all the signals coming out of our Tekonsha going through the adapter, coming out to the 7-way, and we can have it right by our hitch ready for us when we need to tow. Now I do want to mention, typically our wiring is not going to be installed in this area. Most people are going to be installing it on the hatch, because that's where the lights are.

But again, the problem arises when you want to put a 7-way on your vehicle, you have to route the 4-pole wire somehow down the hatch, down the body, and then get it out to the outside. But I found a much easier way.So if you are going to be installing a 4-way, you can still do it right here. Or if you're going to be putting a 7-way on, it's still much easier to install it this way. And we'll give you a few tips and tricks of how we got everything in place, just to make it that much easier for you. In fact, let's go ahead and do it together now.To begin our installation, we want to open up the rear hatch on our Audi. And we're going to be removing the floor coverings as well as the spare tire. So we can pull up, set this panel aside. And then we'll pull that spare tire out. Now before you go to lift it up, you want to disconnect the electrical connector here. There's two squeeze tabs on the side. We'll pull that out, and kind of just help guide it down through the wheel. So it doesn't get caught. Then you can lift up this piece separately, set it aside, then we'll grab our spare.Now right underneath this panel here is our battery. So we'll lift up on this cover. Just kind of tuck it out of the way. And we'll have these two tabs here, press away from the back and that'll give us access to our battery. Now, at this point, we need to start testing our wiring for our taillights. Now you'll notice that the taillights are on the hatch of our Audi and not on the body. And it is going to make it a little more difficult to test it because typically we would have to pull this panel down to get to the back of the connector, but I already did some checking, and I followed all the wires and they actually come down into this area right here.If we grab this panel where our 12 volt outlet is, let me just pull away. Now, you do want to be careful because that 12 volt outlet kit is on the back, so we'll just rotate it out of the way. But we have this big bundle of wire here. And we already went through and tested which wires are which. And we can go through and let you know which ones are for which function. So the tail light function is going to be a black wire with a blue stripe. It's a rather thin wire, but it's right in this bundle here. And I do want to let you know if you're going to be testing it, you have to have the hatch closed in order for those lights to work. So it will be a little bit difficult, have to have an extra set of hands with you. Somebody to run the lights up front while you're in the hatch.Now our left turn signal is going to be this wire. It's the gray wire with a white stripe. And again, turn your left turn signal on. You're going to have to close the hatch and you're going to want to use the tester that comes in your kit to check this wire, and make sure you're getting that intermittent turn signal, signal and it's lighting up. Now the right turn signal is going to be a gray wire with a blue stripe right here. And it's going to be the same process of testing. We're going to have to have the hatch closed, turn on the right turn signal, and this should blink, or you should get a signal on your tester when the blinker is blinking.At this point, we're going to grab our hardest, and we can start making some of our connections. I'm going to start with our taillight wire. And again, it's going to be the black wire with the blue stripe. We also want to grab one of the quick splices from our kit. We'll get the black wire with the blue stripe, kind of get it out of that bundle so we can get access to it. Push the other wires aside for now. And you'll notice we're going to have an open slot. But on one end, we're also going to have another open slot.You want to slide our quick splice so that our factory wire is going all the way through, just like that. And we'll take our brown wire, we're going to insert into the open slot on the other side. Now it is a little bit of a tight fit in here, but once we have both of those wires in, you'll notice we got that little metal piece on top, when you take a pair of pliers and squeeze it closed so it pierces both of those wires, and it makes a connection and then we can close the plastic cover.But before you squeeze it shut, you want to make sure that all the wires are in the connector and it's not moving around like it is on me now. May help if you turn it around so you can kind of see what you're doing a little bit better. Have that connector on top. We'll come from the other side. And once you have that tab pressed down, not a bad idea to give it a quick tug, make sure it actually pierced through. I'll just take the cover, close it over the top and make sure it locks down.Now our gray and white wire is going to get a hook to the yellow wire in the same way that we hooked up our taillight signal. So open up that quick splice, get everything inside and crimp it down. Now they give you quite a bit of green wire because they expect you to be mounting this on the driver side. And that way you can run it across. Well, there's no need for all of this wire. So I'm actually just going to give myself a little bit of slack like we have with the other ones, and I'm going to cut the excess off.Now the green wire is going to be our right turn signal, and that'll get hooked to the gray wire with the blue stripe, the same way we've been doing it before. Now, if we come back to our converter box, we should have a few more wires left. The red wire here is for our brake signal. However, our Audi uses our right turn and left turn signals as a brake signal. So we don't need to hook up this red wire. That leaves us with our white wire that has a ring terminal, and the black wire with a red stripe. The black wire with the red stripe is going to be our power wire. And this is going to need to get ran to the battery.Now fortunately, it is just a few feet over here, and we can access the positive post really easily. The white wire with the ring terminal is our ground. So we either need to find an existing ground somewhere back here, or we can use the self tapping screw and screw it to a piece of sheet metal. If we look at the very back of that opening, we'll find a couple brown wires that come up to a stud, and that's a factory ground right here. So we can actually just remove that nut and place the ring terminal right over it. So I'll take a 10 millimeter socket, pull the nut off, then take our ring terminal, slide right over the stud, and then reinstall the nut.So we make sure that all the existing grounds are still in place. And if anything did come off, that you put it back in place. Now for our power wire, I'm going to take the butt connector from our kit, I'm going to crimp it onto the end. And we can take the length of wire they give us in our kit. We're not going to need all of this, but just going to strip back the end of it. We can put it in the other end of our butt connector and crimp it down. So now we just need to get that black wire over to our battery.So what I'm going to do is I'm just going to take a couple of these push pins out, so I can loosen up the carpet and the panel here, and try to sneak my wire underneath until I can get into the battery compartment here. Just take a trim panel tool, flat blade screwdriver. We'll pop these pushpins up. I'm going to give us a little more slack to get underneath, see if we can tuck that wire underneath all these panels. Now, there's really not a whole lot of room underneath that panel. So I'm going to go ahead and pull the threshold up and we can try to sneak our wire through the corner here and come back around.So you just grab the rear threshold plate down towards the bottom, lift up. Don't pull too far away because there is an electrical connector on the back. It's going to have two small tabs. We'll squeeze the two tabs together. And we'll set this aside where it won't get damaged. Now that the threshold's out of the way, you can see, we have a pretty clear shot into that panel back there. So I'm going to take my power wire, just kind of start feeding it from back here. You can see it's just going to pop right out. Just want to make sure you pull the slack through, and get all the wire to the inside.Now I'm also going to take my 4-pole connector, and I'm going to route it the same way towards the battery in the center, because we're actually going to be mounting our 4-pole on the outside. So again, just kind of take that same path, might be a little more tight of a fit, just because of the connector on there, but we should be able to push it through. Going to grab it with our finger on the other side, pull all that slack through. And before you pull too much, you want to make sure that you have your converter box mounted because we have plenty of slack on this side of it, but we don't want to pull on these wires too much. And we also don't want our converter box flopping around getting banged into things.So I think I'm just going to take a couple zip ties and I'm going to zip tie it to some existing wiring back here. That way it'll be nice and protected, and it'll fit behind the panel. Now if we move over to our battery, we're going to have this little tab, push towards the front of the Audi, lift it up, and you are going to want to grab this small piece here, lift straight up, it'll come right off. And that'll allow you to pivot the cover open so we can get access to the stud right here. So we're going to route our wire so that we can get it into the battery compartment here. Kind of estimate about how much we need. However, I'm going to cut it a little short because we're going to add in a fuse holder to make sure that our wiring is fuse protected.Now we can take our fuse holder, I'm going to cut the wire in half. I'm going to strip back both ends. On one end, we want to put another one of the butt connectors, just like we did before. We'll crimp it down. And on the other open end, we're going to put on a ring terminal. You just want to grab whichever ring terminal is going to fit around the stone on the battery. So I'll slide that in place and crimp it down. We'll take the open end of our power wire, strip it back, we'll crimp it right down into the butt connector.I'm going to grab a 13 millimeter socket, and we can remove the nut that's on the positive post. At this point, you want to make sure that your fuse is not in place in the fuse holder. But we'll slide the ring terminal over, and we can tighten down that nut again. Now in order for us to get our 4-pole wire to the outside so we can mount up our adapter, we're going to need to go through an existing grommet or make a hole. Now, fortunately for us, we do have an existing grommet just to the passenger side of the latch mechanism, just right below it. This rubber grommet here, if we push, it should fall out and fall on the ground. Then we can get started feeding our 4-pole connector through. I will let you know, it's a little bit of a tight fit, but it will fit through, just going to have to work around the dust cover and make sure that ground terminal doesn't get damaged.Push it through until we can get access and let all the slack fall down. Now, obviously that grommet was there for a reason, we don't want to leave a hole in our car. We don't want any exhaust fumes or any other kind of leaks to come inside. So what I'm going to do is I'm going to take a pair of cutters and I'm going to cut a notch or a slit, right to about the center of my grommet. That way I can slide it around my wire, have it go through. Then we can push that ground back in place.And I always suggest to seal it back up with silicone, again just to make sure no water or fumes are going to get inside. Just going to cover the entire area, seal it up with some silicone. And the kit's not going to come with silicone, but if you do need some, you can pick it up here at Now that all of our connections are made inside, and we have our 4-pole routed to the outside. I want to make sure that they're working before we start putting everything back together.So I'm going to take the 15 amp fuse, put it into the fuse holder and then I'm going to take my 4-pole tester and verify that all my signals are working. So now if I turn on my headlights, we can see that our taillight function is working, as well as the left turn signal, the right turn signal, and our brakes. But now that we know that all of our circuits are working properly, we're going to go ahead and clean up all the wires and put all of our panels back in place on the inside. And then we're going to move down underneath and get our adapter in place.If you're only going to be using a 4-pole, then all you really need to do is put all your stuff back. Now in order to mount our 7-way. We did need to mount the bracket. Now the bracket does come with the adapter. However, depending on which hitch you have, you'll notice real quickly there's not a whole lot of room to Mount the bracket. So we used a long bracket, and at the very bottom of the trunk pan, there's a flange right here. We actually just drilled a couple holes into our bracket and through that flange and then put a couple of lock nuts on the back side so we have a nice secure mounting point.We can take our adapter now, and we want to feed all the wires through the opening. So feed the 4-pole connector as well as all the wires with the butt connectors on them. And you do even want to send the other 4-pole that's coming out towards the end of it through. Push the 7-way in, grab the 4-pole. And this is actually just going to slide right into this notch here, going to be held in place by friction. Just going to sit just like that. We want to grab the hardware that comes through our 7-way. We'll have some screws or bolts and some lock washers. Put our lock washer over the bolt, go in through one of the mounting holes, make sure it goes all the way through to the back side of the bracket. Then we'll take a flat washer, put it on the back. Then we'll grab one of the hex nuts and put that in place.This will be the same combination for all four, so we'll get the rest of the hardware in place. Just come back with a Philips screwdriver and a 3/8 wrench to hold the nut on the back, and just tighten up all the hardware. Now I did pull that 4-pole bracket, or the 4-pole wire out of the bracket, just to make it a little bit easier to reach those nuts on the back, so we can easily just slide it back in place when we're done tightening it up.Now, coming out of the back of our 7-way, we're going to have our 4-pole adapter. We're going to open it up and you're going to notice real quick that it's the exact opposite of our vehicle end. So just want to plug these two together. And what I like to do to make sure this connection is nice and solid, is I'm actually going to poke a zip tie through the connectors themselves, wrap it around, and then also wrap everything up with electrical tape. This will just ensure that our connection is going to stay together. I won't have to worry about it coming apart. And the electrical tape will help any moisture, hopefully from getting inside the small gap, if there is any separation between our connectors. And as far as the dust covers go, you can leave them on, or you can cut them off. Since this is going to be a kind of a semipermanent connection, there's really no need for them, especially since we're going to be taping it up.Now on the back of the 7-way we're going to have four more wires, three of them will have butt connectors and one of them have a ring terminal. The black wire with the butt connector is the 12 volt power source. So you can have 12 volts at the back of your 7-way. The yellow wire is going to be for your reverse light circuit. If you'd like the reverse light circuit to work, or if your trailer has reverse lights. And the blue wire is going to be the brake output signal for your brake controller. Now our Audi does not have a brake controller, and we don't need any of the other functions besides our lighting functions. So we just need to hook up our ground wire.So I'm going to end up talking all my wire pretty high up. So we don't see all this bundle of wire down here. So for now just going to start working it towards the top, kind of tucking it away. That way I can also see how much room I'm going to need for my ground wire, and where I can attach it. Now we have a nice spot of flat sheet metal where it actually doubles up right here, right above the opening where our hitch is, and we could attach our ground wire right in this area. I will let you know, it's a little bit of a tight fit to get a full sized drill in there. But if you either have a swivel, an extension, or a right angle drill, it'll make it a lot easier to get that self tapping screw started.So we're going to put our ground wire right around in this area. I'm going to take the self tapping screw and a 1/4 nut driver. And I'm going to get it started in place first. And then I'll put my ring terminal around it. Just want to double check the ring terminal is nice and secure and it's not loose spinning around or anything, but also want to be very careful not to strip out the self tapping screw. So I'm going to go ahead and put a little bit of electrical tape on these butt connectors, because we're not using them, but we also don't want any moisture to get inside and start going all the way back to the 7-way causing corrosion.So I'm going to wrap everything up with some tape. Then we just take some time clean up all the wires under here, and find a nice spot to zip tie them up out of the way. The final step of our installation is making sure that our wiring is still working and the 7-way's going to work properly. So I've got my 7-way tester hooked up. You can see that my taillight function works, as well as the left turn signal, the right turn signal, and the brakes. All we have left to do now is hook up to our trailer and hit the road.

Questions and Comments about this Video

Nick V.

I just completed all the install and everything works great now my question is how to wire the two extra wires for trailer brakes I purchased a curt echo Bluetooth and when I plug it in no light turns on so I don’t have power

Etrailer Expert
Reply from David B.

Great job on the install. Check out the linked articles on routing the power wire and wiring a 7 way plug.


I just did this install today , did exactly what is described in the video step by step. When it came time to test it, I got a warning on my dash about light fault, and my tailights are not working at all anymore. The bumper lights and third brake like still work ( and the bumper lights still work as turn signals when using turn signal) but main tailights don't work. It's grounded same spot as video , power run exactly the same way ect. Thoughts?

Etrailer Expert
Reply from Les D.

@Sam, What is the year, make, and model of the vehicle that you have, and year, make, and model of your trailer? Does your vehicle or trailer have LED lights. I assume that when your trailer is disconnected from the tow vehicle that the vehicle lights work normally? Regarding grounding, I would file the connection spots clean and shiny to bare medal, both on your vehicle ground and your trailer ground. Take a look at the attached article as well.

Reply from Sam

Hey so I thought I would update, I actually figured it out! Forgot to reconnect the sensor in the scuff board before putting it back, and if you don't do that nothing works ( also gotta start the vehicle for it to recalibrate) but it works great !

Etrailer Expert
Reply from Les D.

@Sam, Good troubleshooting!

Pam M.

My installer ran the wiring through the door casing and it is a huge pain to have to run it through the door (Audi Q5). I also have issues keeping the brake control connected. Is it possible to get the wiring set up outside like other vehicles that come ready to tow?

Etrailer Expert
Reply from Jon G.

If you have a rubber grommet in the bottom of your trunk somewhere then you should be able to cut a slit in it and feed the 4-Way through and to the hitch receiver. You'll want to seal up the rubber grommet once you've fed the connector through and then secure it to your trailer hitch using the no-drill bracket # 18136 and then part # 18144 or # PK12711U depending on if you have a 4-way or 7-way.

Daniel C.

Thank you for this video, it's exactly what I needed! I'm wondering about the black wire going into the 7-way adapter. I see in other installation videos where they do go through the effort to connect that to the battery with a 30 or 40 amp fuse. I would like to know if I need to do that in order to make the 7-way adapter work with the Curt Echo Wireless Trailer Brake Controller, C51180. The documentation for that break controller seems to require that 12V to be connected: Am I missing something?

Etrailer Expert
Reply from Chris R.

You are correct - that black wire will need to be run up to the battery (via a breaker) to activate the 12V circuit. The Curt Echo Brake Controller # C51180 does indeed need this circuit to be active for operation.

Info for these parts were:

Employee Jeff D
Video Edited:
Jeff D
Employee Chris R
Video Edited:
Chris R
Employee Robert C
Test Fit:
Robert C
Employee Aidan B
Video by:
Aidan B

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