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Trailer Wiring Harness Installation - 2008 GMC Acadia

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How to Install a Wiring Harness for a Trailer on a 2008 GMC Acadia

Today we are going to be installing wiring harness part number 118451 on a 2008 GMC Acadia. OK, we are here at the back side of the vehicle and the attaching points for our wiring harness are actually located directly behind the tail light assemblies themselves on both sides of the vehicle. So the first thing we want to do is to go ahead and remove them. There are two black caps on each one of the assemblies. You need to pop those back, and that will give us access to the fasteners that are holding the tail light assembly on. We are going to remove those fasteners and pull the tail light assembly off to gain access to the connectors themselves. We just take a little flatheaded screwdriver and pop that right back. And as you can see, there is a regular hex head screw in there. And you want to be careful when you are doing that to make sure you do not break the locking tabs. And we are just going to take a little 7-millimeter socket here and remove the bolts. With both screws removed, we want to go ahead and gently pry away the tail light assembly. There are two aligning tabs here on the back side. You want to make sure that those do not break. You just want to gently kind of wiggle it back and forth until they release.

And you can see here on the back side of the tail light assembly the connector that we are going to be plugging into. What we want to do is release the tab here. I am just going to use a little flathead screwdriver. And I am just going to gently pry back just a number of releases. Our T-harness is going to plug directly in-line here. Here on the drivers side, we want the connector with the yellow and brown wires to plug in-line here. We are just going to plug the black side into the brown connector until it clicks and we are going to plug the brown connector into the back of the tail light housing. And again you want to push that in until it you hear the click. All right, as you can see here there is an opening in between the back of the vehicle and the bumper here. And we are going to feed all our wires down below there and route it over the green wire piece of the harness all the way over to the passengers side. And as you can also see there is a ring terminal that we are going to use for our grounding point. And there is a self-tapping screw that is provided in the installation kit, and we are just going to screw that directly into the back side of the metal here.

OK, with the ground screw and ground wire mounted into place here, I am going to go ahead and fish the green connector down through the opening here between the bumper and the body and over to where the passengers side tail light assembly is. I am going to actually use a piece of what is called stove wire because it is a very tight space in between here and the connector and you might get hung up if you just try to it in there. So I am going to use a piece of stove wire and feed it down through to use it as kind of a leader. And I am just going to go ahead and tape my connector to the end of the stove wire, and again it is just going to help me feed it through the opening in between the body and the bumper and make that a little bit easier. And with the connector fed down through I am also going to do the same thing for the 4-pole end of the harness because it needs to go down and below as well. And with all the wires fed through down below, I can go ahead and put the tail light assembly back on here the drivers side. You want to make sure that you kind of manipulate the connector a little bit so that it does not get pinched when you put the tail light assembly back on. I am just going to snap our covers back on.

And now we can go underneath the vehicle here and we can show how we are going to route the wires over to the passengers side. Both wires I am just routing behind the bumper fascia here. The 4-pole, I am just going to route over here and kind of tie off here on the tow hook. When routing the wire, you definitely want to make sure you avoid any possible pinch points where the wire can get pinched. Or route it away from the exhaust itself, as well, which will get extremely hot. And I am going to do the same thing that I did on the drivers side, which is to route the fish wire up and through the opening, up to the passengers side tail light, and then tape it to the harness and use that to help pull it up through the body area here. We are just going to go ahead and make our connections here as well. And we are just going to pop the covers back on, just like we did on the drivers side.

And that pretty much concludes our installation. I am going to back underneath the vehicle now and just double-check all the wires, to make sure they are up tight and out of the way - again, away from the exhaust or any kind of possible pinch points. You can see the green wire here is still kind of close to the exhaust. I am going to to ahead and pull that back behind the bumper here, behind the fascia. I am just going to secure the excess 4-pole wire here to the hitch itself. Once you are satisfied that the wires are up and out of the way, your installation is complete. And that will conclude the installation of wiring harness part number 118451 on a 2008 GMC Acadia.

Info for this part was:

Employee Zack K
Video Edited:
Zack K
Employee Joshua S
Video Edited:
Joshua S
Employee Chris R
Video Edited:
Chris R
Employee Patrick B
Test Fit:
Patrick B
Employee Cole B
Installed by:
Cole B

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