Trailer Wiring Harness Installation - 2016 Mazda CX-9

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How to Install a Trailer Wiring Harness on a 2016 Mazda CX-9


Today on our 2016 Mazda CX 9, we'll be installing Tekonsha T1 vehicle wiring harness for the factory tow package. This will will give us a 4-pole flat trailer connector. Part number 118278. When we've arrived at our and we've unhooked from our trailer, we can replace the dust cap on our wiring, open our hatch on up, open this compartment on up, and store our wiring inside of it. It's tucked up out of the way, we don't have to worry about any of our cargo damaging it, and it's there for when we need it. Whenever we want to use our wiring, we just got to lift up on this cover, lift it out, set it to the side of our trunk latch, put it down by our hitch, and then close our trunk on up. All right, here's what our wiring harness comes with. We have our wiring harness here with a plug that goes to the factory tow package wiring in our rear hatch.

There's a ground wire we'll have to attach to the vehicle's chassis with the included self-tapping screw. The wiring then goes to this module like converter here which will isolate our trailer wiring from the vehicle wiring so we don't worry about any voltage being back-fed into the vehicle if there's a short in our trailer. We have a length of wire here. If I got to our trailer connector, it's a 4-pole flat to give us all the lighting functions required by law. Has a built-in dust cover here to help protect our connector.

We have some double-sided tape to attach our module to the side of the vehicle, and then several zip-ties here in order to secure our wiring out throughout the vehicle. Now that we've gone over what's included, we'll show you how to install it. Start by opening our rear hatch. Remove our floor covering here. We just slide it forward over our third row seat if it's folded down just to get it out of the way. Take out these side panels.

Take out this carpet here that goes over our spare tire. Take out these plastic trays. Slide them up and out of the way. Pull up on them to release the passenger side. Take our jack out.

Take out this panel here. Just pull up on it, pull it out. Pull up on our threshold cover here to release it. Set it aside and out of the way. Take off this plastic pushpin here. Use a flat head screwdriver to get it out. Pull up on it. Center pulls up, you can pull the whole thing out. Fold our cargo loop on down on the passenger side here. I pull down on this cover here. We'll access this 10 millimeter bolt. Remove this bolt. I'll remove the cargo hook. Make sure we push this back together first. It's back together. Put the bolt in it and I'll set it aside. I'll do the same for this one right here. It's slightly different. Pull up on the lever and you find the 10 millimeter bolt right there. Pull that out and set it aside. Now we'll pull back our passenger side panel. Use a trim panel tool and come behind. This will help get a grip in it. Do the same for our carpet. Now just pull this forward a little bit. Now our unused connectors are right behind this panel and that's where we'll plug our harness on into. Once you hear a click, pull back on it, make sure it's secure. Now we need to attach our ground wire. We can use the provided self-tapping screw and secure it to the chassis on this area. Right here, there's a 10 millimeter bolt that's being used as a ground location. To remove that bolt, we can place this underneath the bolt and secure the bolt. We don't have to drill any holes into our vehicle. That bolt removed. Stick the wiring harness on there and resecure it. Okay. Now I pulled off the back on one side of our double-sided tape. Apply it to the back of our module box. Press it down and make sure it's secure. Peel off the other end and I'll apply this to the flat surface inside our vehicle. Now push down on it, make sure it's secure. Now we'll take our wire, and run it underneath this panel here. Just set it inside that spare tire wall, and we'll push our panel back into position. Make sure your weather stripping sits on top of it all the way. Your pushpin, reinstall it. You reinstall our cargo net tie-down points here too. We'll reinstall this piece here. Make sure it lines up with the holes. Push it back on down just like that. Reinstall our jack. Okay, we'll reinstall our sill plate at this point. Just line it up in its holes, push down until it snaps down into place. Make sure that weather stripping is sitting on top of it all the way. We'll reinstall our side panels now. Just kind of drop down into place like that. Driver side one, you got to physically push in like that. Pull our wiring out and set it to the side here. We'll reinstall our spare tire cover just like that. The wiring, we can rest inside this compartment right here. We'll resinstall our side panels just like that. We'll resinstall our cover for our compartment just like that. That completes our installation. If we ever want to use our wiring, we just got to lift up on this cover, lift it out, set it to the side of our trunk latch, put it down by our hitch, and then close our trunk on up. Now before we hook up to our trailer, it's always a good idea to test our wiring and make sure it works. We'll take our dust cap off here. We'll be using a 4-pole flat trailer tester. It's part number I26. We have these available on our website if you want to purchase one. Just push it on in there and we'll test our function inside the vehicle. All right, so with our headlights on, you can see that the red LED that corresponds to the brown wire is working, we'll do our left turn signal now. I'll do the right. I'll step on the brakes, and you can see the LEDs for both the yellow and green wires are now illuminated solid. Now that we verified that everything's working, we can go ahead and hook up to our trailer and get on the road. That completes our installation of Tekonsha T1 vehicle wiring harness for a factory tow package with 4-pole flat trailer connector, part number 118278 on our 2016 Mazda CX 9.


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Info for this part was:

Video by:
Andrew K
Video by:
Kathleen M
Video by:
Jonathan Y
Video Edited:
Jacob T
Video Edited:
Chris R
Installed by:
Cole B
Test Fit:
Brent H
Test Fit:
Robert C

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