Fifth Wheel and Gooseneck Wiring Harness Installation - 2018 GMC Sierra 2500

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How to Install the Fifth Wheel and Gooseneck Wiring Harness on a 2018 GMC Sierra 2500

Hi there, GMC Sierra owners. Today on our 2018 GMC Sierra, we're going to be installing Draw-Tite's fifth wheel or gooseneck wiring harness. This wiring harness is going to put your seven-pole connector in a much more convenient location for your fifth wheel or gooseneck trailers. Often, your fifth wheel gooseneck trailer, the cable that comes with it isn't long enough to reach over the back of the bed of your truck to plug into your existing factory connector. And if it is long enough, it's usually just barely long enough and then you've got a cable rubbing up against the outside of your tailgate potentially scuffing up the paint.This keeps everything in your bed, doesn't put any stress on the length of your cable, and your factory seven-pole connector still functions along side with this one. The seven-way connector has a spring-loaded cover with rubber gasket on the inside to keep out any dirt, debris, and moisture, ensuring a long lasting connection.You will have to drill a hole to mount your seven-way connector.

After that, it comes with everything you need to get it installed. We'll begin our installation at the back of our vehicle. We're going to choose the location where we want to put our seven-way connector. We're going to be placing our here, just in front of the tailgate on the driver's side. I've gone ahead and marked it out.

I just did this by placing it backwards on there, drawing a square around it, then an X to find the center, and we'll use a two-inch hole saw to cut out the hole for our connector to slide into.We can then clean up the metal shavings and use some general purpose cleaner to clean up the marks we made, and we'll use some Klear Kote to seal up the exposed metal to prevent any rust and corrosion. We can then insert our connector into the hole that we cut. Kind of get it level and then install one of the self-tapping screws that come in the kit. You're going to need a quarter-inch socket to install it. You'll probably need to go back and readjust it a little bit.

Make sure that it stays level. And you can just install the rest of your screws.We're now underneath the vehicle and if you look up here, you can see where are connector's poking through, so we'll just reach up and plug in our connector from our wiring harness. We're going to use the end that has a single connector on it for this side. You can then take the excess slack out of your wiring. We're going to route it up over the frame towards our existing seven-pole connector.We're now on the backside of our existing seven-pole connector.

You'll see the plug here. There's a gray locking pin that needs to be removed. So you'll need a screw driver to push that locking tab out. It can be a little tight. You can take your spare tire down to give yourself more room to work, but it's not necessary to take it down. Once the lock tab's been pushed out, we can push in on the release tab, and pull our connector off.We'll now take our new harness and it's going to simply plug inline between our factory connector and our factory seven-pole connector. This will allow us to use both our factory and our new seven-pole connection. Once you've got them plugged in, make sure to push the lock tab back in on your factory connector, and you can use the included zip ties to tie up the excess wiring.Now, with our wiring all cleaned up, we can test out our new connection and verify that everything's working. We've now got our tester plugged in so we can check everything out. You can purchase these testers here at or you could just plug your trailer in, because it's just going to show us our lights and if they're working. Your trailer will tell you the same thing. You want to make sure you have your left turn signal, right turn signal, tail lamps, and brake lamps. If you have a brake controller, you'll want to move the manual slider, and you can see our trailer brake needle moving here. And then you also want to make sure that your charge line is putting out 12 volts. We'll check our charge line circuit and we're all good. You can test your charge line with a simple test light at home.With everything working properly, we're ready to hook up our fifth-wheel trailer and hit the road. And that completes are installation of Draw-Tite's fifth-wheel or gooseneck wiring harness on your 2018 GMC Sierra.

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