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Trailer Wiring Harness Installation - 2014 Volkswagen Passat

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How to Install a Trailer Wiring Harness on a 2014 Volkswagen Passat

Today on 2014 Volkswagen Passat, we'll be installing the tow ready, upgraded, heavy duty modulite vehicle wiring harness, part number 119190KIT. We're going to first need to remove the trunk lining and then we'll need to remove this rear threshold piece. In order to remove the rear threshold, we'll either take a trim panel removal tool or a large flat head screwdriver. We'll work it underneath the trim piece and pop it upward. Next we'll remove both of these foam pieces. Next we'll remove this little panel here, set it aside.

Then we'll need to remove four hex key push fasteners. There's one up here, and three along the back edge here. Now that we have those four removed, we'll peel this carpet piece back. We'll check and see which wire does which function. We'll connect it to the black wire with a white stripe. We'll turn the left blinker on, and turn that off.

Now step on the brakes. Turn it off. So you can see the black wire with the white stripe is the left turn and brake signal. I will figure out which one is the running light circuit. There's our running light circuit.

That is the gray wire with the black stripe. We'll be connecting the yellow wire off the converter box to this black wire with the white stripe, and the brown wire to the gray wire with the black stripe. Go ahead and take one our quick splice connectors, put it onto our gray wire. Take the brown wire from the modulite box, take our pliers and crimp it down. Once it's crimped, you can close the top. Then repeat that same process for the black wire, where we'll connect our yellow wire in.

Next we're going to add the ring terminal here to the end of this red wire. Since this system is a two wire system, this red wire will get ground with the white wire, to the vehicle's body. Strip some wire back, then we'll add our ring terminal in, crimp it down. Next we're going to take the long black wire that comes with the kit, strip one end back and we'll be using a butt connector to connect it to black wire coming out of the converter box. We'll take a little electrical tape, and tape up our connection. Next we're going to take the two sided adhesive tape and attach it to the back of our converter box and then we'll attach it to the interior of our trunk here. Peel off the one side, and we'll attach it to the back side of the box. Peel off the other side, then attach it here to the inside of the trunk of the vehicle. Next we'll ground the white and the red wire here to the vehicle's body. Good idea to try to find an area that the metal is doubled up on. From over here on the passenger side, we'll just repeat the same process for removing the hex head push fasteners. We'll take our tester light again, test this dark gray wire with a red stripe on it. We have our turn signal on right now. We're tying the green wire in with this dark gray wire with the red stripe. We'll route our green wire over here to the passenger side. We'll take our quick splice connector and we'll put it onto the gray wire with the red stripe first, and we'll connect our green wire into that. We'll crimp our wire down once we have it in place, and close the top clasp on it and we'll put our passenger side back together. Next we're going to take the long black wire, we're going to need to run up to the front and connect to the battery. We'll pull that out from underneath the side panel here on the driver's side, as well as our four flat wiring. That done we can put our panel back in place over here. Go ahead and put our center threshold piece back in place as well. We've folded down the back seats to make things a little easier. I'm going to use this rubber grommet right here, we're going to put a small little slit in it and then we'll pull our black wire that runs up to the battery through it. Just going to take a little razor knife here, put a small slit in it, and then take our black wire and feed it through. Now that we've pulled our wire down from the trunk, we'll route our wire up to the battery. When routing the wire, you want to make sure you stay away from any areas that may move, have sharp edges, or become hot, as all three of these could easily damage the wire. We'll also be using some zip ties to help secure the wire along the way. Now that we have our wire routed up towards the front of the vehicle, we'll trim off any excess zip tie. Now we'll take a pull wire here from underneath the hood, and feed it down underneath the vehicle. Our pull wire is just an old section of airline tubing that we're using. Now we'll connect our black wire to our pull wire here underneath the vehicle. We'll go back up here into the engine compartment, take our pull wire and pull our black wire up into position. Now that we have our black wire pulled up into position, we can cut it to length. We'll then take our fuse holder, cut the loop on it, strip one side back, add a butt connector to this side, crimp it down, then take our black wire here, strip a little bit back, connect it here to the other side of the butt connector. The other half of the fuse holder, we'll strip a little wire back and we'll be adding a ring terminal to that. You can crimp it down then. Now we'll tape up our connection here. Next we're going to snip out the section here of this ring terminal. Next we'll loosen up the nut here that holds the positive side of the battery tight. We'll then take the portion of the ring terminal that I snipped out here, so it'll slide in just like that, then re-tighten down the nut. We'll then install our ten amp fuse into the fuse holder here, and then we can close the lid. We're going to put one zip tie back here, and trim off any excess zip tie. Then we can cover our battery back up. We can then put the rest of our trunk back together. Now we'll show you where we store the four flat when not in use. We do keep in stored inside the vehicle, as it does help it last longer and helps protect it from the weather or any corrosion. Now we'll show you how you would use your four flat. You simply lift up the trunk cover here, making sure we stay away from the center latch area, fold it down along the bumper, and you can simply close the trunk on it and the weather stripping will push in and will not damage the wire. When you're not using your four flat, you simply take it back up, lift the center cover and you can store it in along the spare tire. Now we'll test our four flat using our test light. We'll connect our ground from our test light to the open prong on the four flat, and we'll turn the running lights on, where we'll touch the brown wire. Our left turn we'll touch the yellow wire. Our right turn we'll touch the green wire, and for brakes we'll touch the yellow and the green. As you can see here, all of our functions are working just fine. That will do it for our installation of the tow ready, upgraded, heavy duty modulite vehicle wiring harness, part number 119190KIT on our 2014 Volkswagen Passat. .

Questions and Comments about this Video

Carl W.
Why cant I just connect the wires to the proper wires without this box. If the turn signal, and brake lights are on the same wire, wouldnt that work without the use of this box?Thanks
Etrailer Expert
Reply from Patrick B.

Not on a 2014 Passat. The circuits for the tail lights on the vehicle have a minimal current capacity, a trailer would over load those circuits and blow fuses or damage the tail lights or factory wiring. The box pulls in a separate power feed to support the current needed for the trailer lights. Also modern VW vehicles and other European makes use various types of electrical systems, Pulse Width Modulation or Multi-Plex, and these boxes are needed in order to process those signals.

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