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Trailer Wiring Harness Installation - 2004 Volvo XC90

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How to Install a Wiring Harness for a Trailer on a 2004 Volvo XC90

Today on this 2004 Volvo XC90, we will be installing the modulite wiring harness kit part number 119190KIT. We are inside the cargo region of the vehicle here. We are going to need to go ahead and dissect most of the rear to gain access to wiring points that we are going to be attaching to. The actual connection points are located behind the interior panels here. To gain access to those, we are going to need to start by removing the cargo floor here and release the straps on each side. Then we can just take the handle here in the center and pull that up. If you want to just set that off to the side for the time being. Next I am going to remove the corner cover here. Then next we want to remove this interior panel here. 00:40

With the access panel removed, you can see there are two allen type screws that are holding the tail light assembly onto the vehicle. You have got one here and one right here. To remove them I am just going to take a pair of vice scripts, them over and I am just going to unscrew it like a normal screw. And with those two removed, we can come back out to the outside of the vehicle and pull the tail light assembly off. As you can see we have got multiple wires feeding the tail light assembly, so we are going to need to test those to figure out which wires we are looking to tap in to. I am going to start by actually taking a self tapping screw and running it to the back side into the metal of the back side of the tail light housing here for our ground wire.01:25.

So, first I am going to test for the left turn function, and it appears to be the green wire here. Next, we are going to test for the running light wire that appears to be the white wire. And then lastly, we will test for the brake wire, and that looks to be our yellow wire here. And those are the three connections we are going to need to make here on the drivers side. You will note that the modulite box itself is fairly large. Now there is not a decent place to mount it here on the outside of tail light assembly, so what I am going to do is go ahead and take these wires here and feed them through this grommet from the inside of the vehicle out, and we will make our connections here. So taking the quick splices provided with the installation kit, we want to go ahead and make our connections to those wires there. The brown here on the harness, switches our running light feed, will connect to the white wire. Our yellow wire is our left turn, which was the green on the vehicle. And then the red wire, brake light, connects to the yellow wire on the vehicle. We previously screwed our ground stud into the back of the tail light assembly, so what I want to do next is take the white wire from the harness, which is our ground wire, strip back a little bit of the jacketing, and take our ring terminal that is provided with our kit, slide that on there, and we just want to crimp that on there. 2:43

With those components hooked up, we can go ahead and put our grommet back in, reinstall our drivers side assembly. We are back inside the vehicle here and you can see our modulite box is kind of hanging freely from where we made our connections through the tail light. There is double sided tape on the back of the modulite box that we can use to adhere it to the inside of the vehicle. Or you can see on the sides here we have got some holes that we can use some self tapping screws to mount to the metal here. Considering its position I am going to go ahead and do that. With the modulite box mounted, we can go ahead and feed our green wire across underneath here and over to the passenger side tail light assembly where we are going to be hooking it up. We can also take the 4-pole as well and route it through that same opening. And then at this time we can also connect our larger lead black wire to the black lead on the modulite box itself. Again we can route it through the same opening that we routed the other two wires through and it is going to be connected directly to the battery. You may notice when routing your green wire across that the lead is not quite long enough for you. If that is the case, you may have to take an extra piece of green wire, like I am going to do here, and just extend it. 3:50

And with our green routed out behind the tail light assembly, we just want to go ahead and connect it to the right turn wire which, again, on this side is the green wire. Okay, we can reinstall the passenger side tail light now. Go back to the center and attach it to the battery. To gain easier access to our battery here, we want to go ahead and remove this protective shroud. There are three screws holding it on. With the battery exposed, we can go ahead and pick one of the terminals here to connect our black wire to. I am going to use the accessory one over here to the side. We just simply want to remove the nut from the top. Then we want to take our fuse holder and we are going to cut it in half. The one side we are going to connect the ring terminal to and that is going to go directly to the battery. The other end we are going to connect the butt connector and it is going to attach to our black lead here. For this larger modulite wiring harness we are going to be using the 15 amp fuse that is provided with the modulite itself. Then we just want to take the wire ties that are provided with our installation kit and go ahead and zip tie up any of the access wire that we may have. Next we are going to put the cover back on the battery then we can go ahead and start reinstalling the interior of the vehicle. Again we are going to leave the 4-pole in the center compartment for the time being and I can show you how we can go ahead and pull that out when we want to use it. With the vehicle reinstalled again, you can see our 4-pole here. When you want to use the 4-pole, you can simply pull it out the rear hatch of the vehicle. The weather stripping here on the back side will prevent the wire from being pinched. And with that, that will conclude the installation of modulite wiring harness part number 119190KIT.

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