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Curt 5th Wheel Wiring Harness Installation - 2015 GMC Sierra 2500

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How to Install the Curt 5th Wheel Wiring Harness on a 2015 GMC Sierra 2500

Hi there Sierra owners. Today in your 2015 GMC Sierra 2500, we're going to be taking a look at and showing you how to install CURT's seven way wiring extension. And this is what our new connector looks like when it's installed. It is located in any location you want to place it in the truck bed. You'll get plenty of length of wiring to go down your truck bed, to plug into the seven way here at the back. You can put it in any location.

I found that I liked the back here as one of the best spots because we don't have to worry about any clearance issues normally with how far our panel sticks out.But the main purpose of relocating our seven way from the back to our truck bed here is for our gooseneck and our fifth wheel trailers. Oftentimes those trailers don't have long enough seven way connectors on them to reach back down the backside of your truck and plug into the connector located where you had it from the factory. By putting it here in the truck bed, you can easily plug in your fifth wheel trailer with the wiring that came included with it, and it also keeps it tucked back and out of the way. You don't want any cords hanging out the back that could potentially fall off the side or get caught on anything, this keeps everything nice and tucked up inside your truck bed.The connector that comes included with it is going to be your standard seven way. It's going to provide you with all of your necessary lighting, which includes your left turn signal, right turn signal, tail lamps, and brake lamps, as well as outputs for your auxiliary charge circuit and for your brake controller.

On the inside, we have a rubber seal that keeps any moisture outside of our connector and the lid is going to be spring loaded so once we're done with it, it automatically seals itself right back up.Now there is some drilling required to get this installed. You will need a slightly larger than a two inch hole saw in order to get your connector mounted up. So I know it is going to be a little intimidating cutting a two inch or larger hole inside your truck, but why don't you follow along with me and we'll go over the installation together so you can have the confidence to do it at home.We'll begin our installation by mounting up our seven way connector. There's four holes in the corners that's going to screw into wherever you decide to mount it and hold it in place, and we're going to need to drill out a hole for the connector to pass through. Now you can place this anywhere you want in the bed of your truck to where it works with your fifth wheel.

You just want to make sure you've got enough room between wherever you're going to put it and the body on the outside. So for that purpose, I'm going to be placing it right here. You can see the body panel here sticks out a little bit further than it does in the other sections here, and this way I know I'm going to have enough clearance between the outside body panel for our connector and everything to fit in there.So now that we know where we're going to be placing it, we're going to use a two and an eighth inch hole saw to cut it out. We're going to be putting it right here in the middle, down towards the bottom of our truck bed. And it's about right in the middle so we're just going to cut our hole now.

Here I've got my file to clean up those edges, and we're just trying to get rid of anything that's sharp around the inside there so we don't accidentally cut our wiring and cause a short. And then we'll take our clear coat to seal it up. Now that we've got our whole prepped, we can go ahead and clean up the mess we made here and we can start installing our new wiring.We're going to start by taking our harness and poking it through the hole that we just cut out. This end's going to go towards your seven pole at the back of your vehicle, and this one's going to connect to our new connector inside of our truck bed. Now we drilled our hole right on the other side of the truck bed here, and all of this is open underneath so we can reach right up in there, so I'm going to reach right up in there, poke this wiring up and then out of the hole to where it comes inside of our truck bed.Here we have our new connector, we just want to poke it through. And that's enough just to where it doesn't fall back down the hole on us. We'll just take that cord now and plug it into our new connector. Just line those up, make sure they click all the way together. I like to just double check, make sure it's not going to come back out, and then we can just push this in. And we're just going to work it down until it sits flat. And then we just want to hold our connector here to where it's level, and then we're going to run the self-tapping screws in that come included in our kit. We'll use a quarter inch socket to do it. Usually, the easiest way to do this is to just run one in first and then level it after that one's in.So I'm just going to go get a rough idea of where we want it be. And now we've got that one in, we can pivot it on that bolt to get it level. Now that we got this mounted up, we can go to the other end of our wiring down below. We're going to route it towards our seven pole connector and get it plugged up. You can see the hitch here, and this is our bumper right there. This is your factory seven way connector right here. We'll need to unplug this because our new harness is going to plug-in line.So first we're going to take our screwdriver here and just pop out the locking tab. That just hooks in there and then the gray piece here will just pop out just like that. Once you got the gray piece popped out, you can reach up here, press in on the release tab and then disconnect the connector. The little gray piece we popped out was hiding the release tab. So it's located just below it. A little hard to see but you can see right there that little black piece, you just press in on that.Now that we've got that disconnected, we can take our factory connector and plug it in. Now, one of the things I do recommend doing is using some dielectric grease on the inside of your connection points and that will help keep out any moisture and ensure a long lasting connection. I've gone ahead and filled up the connector with dielectric grease. If you need some, you can get some here at We're simply just going to take our two connector ends out and plug them together. So the one that we disconnected is a female connector, so it's going to plug into the male on our new harness, sort of bring those up and plug those in. Make sure they click in. I always like to give it a little tug to make sure it's all the way in. And then we're just going to bring the other connector up that's on our harness and plug it right back in to that factory connector.It can be a little tight but it will fit. And make sure that one clicks in all the way as well. And you may have a bunch of excess wiring, they give you plenty of length so you can install it wherever you like. You don't have to put it towards the back like we did. We just wanted to have that clearance room. But if you had another location you wanted to put it, you most likely have plenty of length of wire here to do so. So we're just going to take all this, we're going to bundle it up here, and zip tie it to our factory wiring. We'll use the included zip ties to do so. Sometimes it can be a little bit easier before you zip tie it to the factory wiring, you can just take a zip tie and just get all that excess lumped together so it doesn't come apart on you.With everything plugged in, that completes our installation, but we want to make sure that everything's working properly. So I've gone ahead and plugged our tester into our new seven way connector here in the bed, and we want to make sure that all of our functions are working. Now it's a seven way connector, but one of those is ground. So you need ground for any of these to work, so that's why there's only six lights here, and if none of them lit up, then most likely you got a ground issue.Now one of them is already lit up here, and this is our 12 volt auxiliary circuit. This is mainly used to charge your battery on your trailer, and the rest of them you'll see light up as we go through the functions. You want to make sure you have all your necessary lighting functions which includes your left turn signal, right turn signal, tail lamps, and brake lamps. Now, if you have a brake controller in your vehicle, you can test the last circuit. Now, the small tester that we had plugged in a minute ago will work properly for testing any of the aftermarket brake controllers that we sell here at But for your factory brake controllers inside your vehicle, often they require seeing a load on the trailer for your trailer brakes before it will determine that there is a trailer connected to put an output on it. So unfortunately our little tester here won't work, but our large tester here that simulates a load. You can see that when we push the manual slider, the voltage increases on the gauge indicating that we're sending a signal to our brakes.With everything working properly, we're ready to hook up our trailer and hit the road. And that completes our look at CURT's seven way wiring extension on our 2015 GMC Sierra 2500.

Info for this part was:

Employee Andrew K
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Kathleen M
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Employee Cole B
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