Trailer Wiring Harness Installation - 2014 GMC Terrain

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How to Install a Trailer Wiring Harness on a 2014 GMC Terrain


Today on this GMC Terrain, we're going to install part number 56094. This is a Curt T-Connector Vehicle Wiring Harness with a four pole flat trailer connect. We'll go ahead and cover some of the components of our wire harness. First off, here's a four pole end that will go onto your trailer. After it's installed, there's a cap that goes on to it. Actually take a look at below the four poles split wire harness, the yellow wire goes to the left side, and the green wire goes to your right side. There's two t-connectors.

Yellow goes to left turn, and green will go to right turn. This will fit in between a connection point between wire harness on the vehicle and the taillight. The single white wire with the ring terminal will eventually be attached to the body work behind the taillight for ground. Let's go ahead and install the wire harness. We need to go ahead and open up that back hatch. Now, with the hatch open, we can go ahead and remove the two caps or fasteners to hold the light in place.

A small flat screwdriver to catch the end of the cap. There's a little opening there and pop it open. Two screws behind the caps, use a 10mm socket to remove. The light has to be pulled straight off. There's two snaps here that hold it in place.

Just pull straight back and remove it. I use a simple plastic pry bar. It's pretty wide. I just want to angle right here and gently pull it back so it'll pop loose. Now, we need to go ahead and disconnect the electrical from the taillight. THere's a small tab right here you push down and pull it apart.

We'll go ahead and set our taillight aside for now. We'll do the same thing over on the passenger side. Now, we can go ahead and start to install our wire harness. We'll take the four pole end and drop it down in the opening between the bumper cover and the body work. We'll let that go to the ground, and we're going to do the same thing to the T-Connector with the green wire. Up here, we'll go ahead and take our yellow T-Connector and plug into the factory wire harness. We'll just let that sit for now, and then we'll go ahead and go underneath the vehicle and route our four pole wire to the center of the hitch. Just go right up through one of the safety chain loops, then I'll put the cover for the four pole on to help hold it in place. Now, we'll do the same think with our T-Connector with the green wire. We're going to route it all the way across and to the other side. Now, we'll go ahead and take our T-Connector and route it up from the bottom to the top. I've got a specialty tool for it, but you could also use a piece of wire that'll hold its shape as you push it up through there, or drop it down from the top. The device I used, you can find at any auto parts store if you want. We'll go ahead and plug our wiring harness into the factory harness. Then, we'll take our ground wire and attach it to the sheet metal behind the taillight. The kit comes with a self tacking screw that takes a 1/4 inch hex bit. We'll go ahead and use a couple zip ties to secure our wires to the factory wire and give us working room if you ever have to get back behind the taillight for a bulb replacement. At this point, we can go ahead and reinstall our taillight. Plug the other half of our T-Connector back into the socket for our taillight, and put it all back into place. We'll go ahead and do the same thing back over on our driver's side now. Chances are you're going to run out of zip ties pretty fast. It's always a good idea to get some extra zip ties. Cut off the ends so it won't get in the way of putting the taillight back in. The taillight goes back into place. At this point, we can go ahead and close the hatch on our vehicle and then we'll go ahead and work on zip tying the wires underneath the bumper. I'm going to take my four pole loose and just going to pull out my slack and see how much I have left over, and zip tie our excess. It's personal preference of zip tying your wires from here on out, but I'm going to start off by attaching to the hitch, and then taking care of the slack. Totally optional, but we're going to go ahead and add some new material to help hide the color of the wires. Let's go ahead and just take our excess, hide it behind the bumper, go ahead and put the cap on. Now, we'll go ahead and try it out and verify the functions. We'll take our light tester, we'll ground to the white wire and check the brown wire for a running light circuit. All right, yellow for left turn, and green for right turn. Then, we'll hit our brake signal, which would be a solid signal on the yellow and green wires. Looks like everything works. Okay, with that, that'll finish it for our install, part number 56094. This is a Curt T-Connector Vehicle Wiring Harness with four pole flat on our 2014 GMC Terrain. .


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