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Trailer Wiring Harness Installation - 2008 Lincoln MKX

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How to Install a Trailer Wiring Harness on a 2008 Lincoln MKX


Today on our 2008 Lincoln MKX, we'll be installing the Tekonsha T-One vehicle wiring harness with 4-pole flat trailer connector, part number 118551. All right. When we're ready to hook up our trailer and we've pulled our siring out of our trunk, all we've got to do is make sure our wiring is off to the side away from our trunk latch, we can shut our hatch, and e have a nice, ready-to-use connection down here to hook up to our trailer. We undo our dust cover here, hook up to our trailer, and make sure everything else is attached properly, and we're ready to hit the road and tow our trailer. When we arrive at our destination and we're ready to unhook from our trailer, once everything's unhooked, we can put our dust cover back on here, open our hatch back up, lift up our spare tire cover here, place the wire inside, close our cover, and, as you can see, it's up and out of the way. You don't have to worry about it getting snagged in something when you're loading cargo in and out of your trunk, just close your trunk and it's like it's not even there. All right, here's what our wiring harness comes with. We have our module box here, which will isolate our trailer wiring from our vehicle wiring and eliminate any possible back-feeding of voltages from our trailer into our vehicle's wiring, preventing any damage that may occur there.

We've got these T-connectors, which will tap into our wiring here on our driver's side and then our wiring here on our passenger's side. We have our 4-pole flat trailer connector here. We have where our power is going to hook up, which will run directly to our battery using this spool of wire here, this fuse holder, our fuse for the fuse holder, a couple of butt connectors and ring terminals to make our connections, and a self-tapping screw for our ground wire right here. We also have several zip ties to secure stuff up and out of the way, and we have some double sided tape to secure the box to our side of our vehicle. We begin our installation by opening our hatch. Then we will remove our tail light assemblies using two 8mm bolts here on both sides.

We'll just pull them out towards us, wiggle them a bit, and it'll pop right out. We'll unclip the connector here. We'll undo this one down here too, just so we can get the tail light out of our way. Repeat the same process on the passenger side. With our tail lights removed, we can now take out our trunk coverings here and set it aside. Remove our spare tire ...

lift up on our spare tire surround on both sides. Now we can take off our threshold here in the middle. To do that we just pull straight up on it. Set that aside. Now we'll take our grommet here for our tail light wiring and just pull it on out.

There we go. We'll do the same on the passenger side. Now we'll take a pull wire, just using a piece of old airline tubing we had laying around, go up through our grommet here. I'll reach down behind our panel and pull to the side. All right. Take the tape off of the back side of our module and we'll stick it to our floor over here in the corner so it's tucked up and out of the way. That'll work. Now we'll take our yellow wiring here, tape it to our pull wire we dropped on down. Now we'll take our pull wire and we'll pull our connectors out through our grommet onto our pull wire. We'll take our factory connector here for our tail light and we'll plug it in to the male end here. All right. We'll push in on it until it's secure. You know it's secure when you can pull back on it and it doesn't release. Now we'll take our grommet and we'll cut a slit in it so our wires have a place to go. All right. We're going to feed our black wire down behind our tail light between our bumper and the body of the vehicle so it comes out the bottom. We'll pull our black wire on down. It's sticking out from our tail light pocket; we'll tape it to our pull wire again. We'll go through the hole here that we went in with for our pull wire originally and we'll reach up from behind our panel and pull it on down. We'll pull our power wire into the vehicle. We can undo our pull wire. Take our end of our power wire, strip off some of the insulation. Take one of our yellow butt connectors here, install it on the end of the wire. Don't need that much wire exposed. Crimp this down. Strip off a little more of the insulation on the black wire down here. We'll install our power wire to it and we'll crimp it down. Okay, with that crimped, we now have a secure connection for our power wire. We'll take our ground wire and we'll run it down to the body with a self-tapping screw. Okay, we have a nice solid ground connection with that. Now that our butt connection's been made for our power wire, we're going to wrap our butt connector up in some electrical tape just to help secure it and prevent any contamination, like dirt or moisture, from entering it. Now we'll take our power wire and our driver's side wire, install them into slit we made in the grommet, and reinstall our grommet into our vehicle. With our grommet reinstalled, we'll seal up the slit that we made with some silicon sealant. We have this sealant available on our website if you need to purchase some. Now we'll take our pull wire again, come in through our passenger side tail light . We'll take our green wire and our pull wire and we'll tape them together. We'll pull our wire on up through our tail light housing, pull. With both connectors now out through our housing hole, we can remove our pull wire. With our green wire we're going to zip tie it up out of the way to this wiring harness here, which goes to our satellite receiver module. We'll take our factory tail light connector here and plug the new end with the male end, into it. With all of our connections made we can reinstall our trunk panels now. Start the center one here first, just center it into position, push on down. Take our 4-pole flat trailer wiring, set it to the side here. Reinstall our spare tire surround. Reinstall the actual spare tire. Reinstall our floor covering. As you can see, our wiring will stick out here on the side and it will be easy to use when we need to hook it up to our trailer. When we're not using it, we can just store it in our spare tire well, like that. We can go ahead and reinstall our tail lights now. Plug our reverse light back in; plug our tail light back in using our new T-connector here. Okay. With those both secure, we'll push our assembly back into place, reinstall the two screws. Repeat the same process on the passenger side. Now that our tail lights are reinstalled, we can run our power wire to the front of the vehicle, making sure we avoid any sources of heat or moving parts. I'll go ahead and do that and then I'll show you how I did it once I'm done. We went up and over our exhaust, up and over our fuel tank filler neck, up and over our rear sub-frame, up and over our fuel tank. We secured it to this fuel line and brake line bracket here, just at the front of the fuel tank. We went up and over this plastic plate. Then, finally, secured it to this other bracket here. Now we can use our pull wire again and feed this into our engine bay. We'll take our pull wire here, feed it down behind our brake lines going into our master cylinder, and I'll just push it on down behind all this. We'll come out the bottom and go there and connect it. Here's where our pull wire came down; it's in a great spot right behind these brake lines. Those brake lines will help hold our wire away from our steering shaft right here. We'll just tape this on up. Make sure we get it nice and tight. Now we'll grab our pull wire and pull up our power wire into our engine bay. With all of our wire up in the engine bay, we'll measure off how much we're going to need and cut off the excess. Set that aside. Take our fuse holder, as you can see our wire on our fuse holder is in a complete circle. We can just cut in the middle and strip back both ends . one end we can place a ring terminal, and we'll crimp that into place . other end we can place a yellow butt connector and crimp that one into place too. We'll take our power wire and we'll strip off some of the insulation there. Take our yellow butt connector, from our fuse holder, and we'll crimp it onto the power wire. Take our electrical tape again . If you don't have any electrical tape, but you'd like to purchase some, we do have that available on our website. At this point, since we're about ready to make an electrical connection, I'd like to point out that you have a couple options of doing this safely. One will be disconnecting the negative battery terminal on your battery, or, if you don't want to have to deal with resetting all of your radio presets, just leave the fuse out of your fuse holder when you make your connection to your positive terminal. I'll take a 10mm socket now, remove a nut from our battery post. Place our ring terminal down on, reinstall the nut, place our cover back over our battery post. Take our 15 amp fuse and plug it in the fuse holder and cover up the dust cap. We're going to test our wiring now. I'm going to use a 4-pole flat tester here. We have these available on our website as part number I26, if you'd like to purchase one. Squeeze that on in there. We'll go into the vehicle now and run the lights, and you can see them working. I'm going to go ahead and turn our head lights on. You'll see the red LED that corresponds to the brown wire in the trailer wiring is now illuminated. That will be our tail light circuit for our trailer. If I use our left turn signal, you see the red LED that corresponds to the yellow wire is now flashing. That will be our left turn signal and our left brake light of our trailer. If I do the right turn signal, you see the red LED that corresponds to the green wire is now flashing. That does our right turn signal and right brake light on the trailer. If I step on the brakes, you can see both red LEDs that correspond to the yellow and the green wire are now illuminated solid. That controls our brake functions on the trailer. That completes our installation on the Tekonsha T-One vehicle wiring harness with 4-pole flat trailer connector, part number 118551, on our 2008 Lincoln MKX.


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