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Trailer Wiring Harness Installation - 2009 Ford Focus

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How to Install a Trailer Wiring Harness on a 2009 Ford Focus


Today on our 2009 Ford Focus, we will be installing the Tow Ready T-One Vehicle Wiring Harness with 4-pole flat trailer connector, part number 118457. All right, first thing we need to do on our Ford Focus to install the wiring harness is to open the trunk. Now what we want to do is go ahead and remove the taillight assemblies on both sides of the vehicle. The first step in order to gain access to our taillights is to remove the center trim piece right here. Now with those plastic screws removed, grab one corner of the center piece, pull up on it, and it'll pop off. Go ahead and set it aside.

We can go ahead and remove the panel that covers the left taillight. There are 2 plastic screws on this side, one here and one here. Just go ahead and remove those. Grab the panel at the bottom, and lift up towards the center, pull it out. Once you've pulled it towards the center, go ahead and push it towards the front of the car. Now, with the taillight cover panel removed, we can gain access to the 2 nuts that hold the taillight studs in place.

One's located here and the other one's located here in this hole. Now, using an 11-millimeter socket and ratchet . Now, for the outer one, the stud sticks out a little far on it and it's fairly deep for a deep well socket, so you may need to use a wrench on it to get it started. Using the same 11-millimeter .. Now this one you can actually, since you have access to the stud completely, you can pull the nut off.

The other one we're going to have to let fall down inside the car and take it up once you pull the taillight assembly out. Now grab the taillight on the outer edge and on the inside, wiggle it, and it'll pop loose. There you can here the nut fall down on the inside. Go ahead and pull these and set them aside. Now for the nut that you could not get off because it was recessed inside the hole, the location that it would fall would be right down here. You won't actually have to go looking for it very far.

Now, we'll go ahead and move on to the passenger side of the car and remove the taillight assembly using the same process. Let's go ahead and lay our wiring harness out. The green wire will go to the right side of the vehicle, the passenger side, and the yellow wire will go to the left side, the driver's side. Let's go ahead and set it down on the ground. Come over to our passenger side, we'll take the already removed taillight assembly, and let's go ahead and unplug the bulb, or bulbs, I should say. The bottom one will be your reverse light and this top one here will be your turn signal and brake light. Let's set the taillight assembly in the trunk so it doesn't get damaged. Now I'll just go ahead and start feeding the wires up from the bottom of the car. Okay, that done, let's take the bulb for the taillight turn signal and brake, squeeze here on this connector, and pull the bulb out. Now with the connector and the bulb removed, this is the female end, go ahead and grab the male end of the connector, slide it on in there until it clips into place. Now on the right side of the vehicle, there's also the ground wire, which is the white wire. Use the included self-tapping screw, find a suitable ground location. Right here above the tab where the bumper mounts is a good one. Now, with the ground wire secured, and the connection made to the vehicle wiring harness, we can go ahead and put the taillight assembly back in. First let's put the bulbs back in that we took off. I'm not going to connect this one just yet because it's going to be slightly easier to put the bulb back in the assembly with the connector off. Put it in, turn it, lock in place. Grab the other bulb, do the same thing. Now let's grab the other end of the harness for our tail wires, install it until we hear the click, and then it's in place. Now with all of our connections made, let's go ahead and reinstall the passenger taillight assembly. Make sure we push all the wires down into the bumper cavity as best as we can, and make sure they're not going to come in contact with any of our mounting hardware. Go ahead and put the 2 studs through their respective holes, line up the guide pin here. On the other side there's a little white tab here. Make sure that slides into place with its slot on the taillight. Now, with the taillight assembly back in place, just go ahead and put those 2 nuts back on the studs that they come off of, and tighten them back down. As you can see, with the nuts now tightened back down, the taillight assembly has snugged itself back in in a nice, clean position. With everything done on the passenger side, as far as the wiring goes, let's go ahead and do the driver's side. Pull the assembly down. Let's remove the bulbs, first light on the bottom again. With the bulbs undone, let's go ahead and set the assembly aside in the trunk so it does not get damaged. Now, in order to get the wires up on the driver's side, the easiest way to do that would be to grab something you can pull it up with. I'm just going to use this piece of this air tubing here, so a coat hanger would work, anything of that nature, something that's a little rigid that you can tape the wires to. Just go ahead and route the wire over the crash bar here to the right of it. We'll go ahead and tape our wires to it, and pull it on out. There we go. Just go ahead and remove the tape, set our pull wire aside. Now let's go ahead and make our connection to the vehicle's wiring harness. Grab the male end and plug it into the female end. Now with our connection made to the vehicle, let's go ahead and reinstall our taillight assembly. First let's take the bulb for the taillight, reinstall it on the tail harness until it clicks, insert back into the tail lamp assembly, twist it and lock it into place. Do the same thing for the reverse light. With that done, let's go ahead and reinstall our tail lamp assembly. Let's go ahead and reinstall our nuts on those 2 studs. Now with our taillight assemblies reinstalled, let's go ahead and put all the panels back in the trunk. There's a clip right here and 2 studs here. Go ahead and slide it on into position, line the pins up, and give it a tap back into place. Take your weather stripping and make sure it fits on top of it. I'm just going to grab our plastic pins and screws and reinstall those. There's one there and one here again. Same thing here on the left side. We have the clip and the 2 guide pins, reinstall those. Now we can go ahead and reinstall the center trunk panel. Go ahead and rest it into position, tap it until it clips into place. Let's go ahead and get the weather stripping going back over it so it secures itself properly, and we can get the push pins in. If you don't get the weather stripping on top of this, it doesn't sit back far enough. Let's go ahead and grab our plastic push pin retainers and go ahead and reinstall those. Now with the taillights and the trunk panels back in position, and everything in place and secure, we can go ahead and close the trunk, and continue on with the installation by tidying up the wires underneath the bumper. Now with the excess of wire we have for our trailer harness connector, the easiest way to do this for a clean installation is just for temporary use, go ahead and stick the connector with the dust cap on it, around the safety chain loop on your trailer hitch. Then we can gather up the rest of the wire, pull it nice and tight and zip-tie it to the back of the trailer hitch to secure it. Then we will go ahead and bundle up our excess wire, grab a zip-tie, go ahead and secure our excess nice and tight, and secure the bundle itself. Now with our wires secured to the trailer hitch, let's go ahead and cut off the excess zip-ties just so we don't have to listen to them rattle around anywhere. Now with our wiring all installed, it's a good idea to test everything out and make sure it works before we go hook it to a trailer. Let's go ahead and start with our taillights and running lights, which will be this brown wire here. I just went ahead and grounded to the connector on the harness itself, which is grounded to the body of the car. As you can see there, we've got a good signal. Now let's go ahead and do the left turn signal, which will be the yellow wire here. As you can see that's flashing. Now we'll go ahead and switch over to the right turn signal, which is the green wire, and that's flashing. Now, let's go ahead and do the brakes. Go ahead and step on the brake, please. The green wire there works for the right side brake light, and the yellow wire works for the left side brake light, and that will complete the installation of the Tow Ready T-One Vehicle Wiring Harness for 4-Pole Flat Connector, part number 118457 on our 2009 Ford Focus.


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Info for this part was:

Employee Joshua S
Video by:
Joshua S
Employee Dustin K
Video by:
Dustin K
Employee Jacob T
Video Edited:
Jacob T
Employee Andrew L
Video Edited:
Andrew L
Employee Rick A
Test Fit:
Rick A
Employee Brent H
Test Fit:
Brent H
Employee Cole B
Installed by:
Cole B

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