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Trailer Wiring Harness Installation - 2015 Ford Mustang

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How to Install a Trailer Wiring Harness on a 2015 Ford Mustang


Today on our 2015 Ford Mustang, we're going to review and install the Two Ready T1 Custom Fit Vehicle Wiring Harness with 4-Pole Trailer Connector, part number 118487. Now we'll go ahead and review and show you the operation of our 4-flat trailer connector. Our trailer connector gets stored inside down in the spare tire well. We'll simply take the 4-flat connector out, run it out over the threshold, staying away from the truck latches pinching it off in the latch, can't harm the wire. However, the weather stripping is thick enough that we can simply close the trunk on it. Then, we'll run the 4-flat connector down to our hitch or address.

Then once we're finished, we simply open up the trunk, roll up our wiring, and store it down in the rear cargo area. The 4-flat trailer connector will duplicate the manufacturer's running, turn, and brake signal circuits on our trailer. The standard 4-flat connector will fit many applications. Now let's go ahead and show you how to install it. To begin our install, we're going to go ahead and open up the trunk, and then remove the spare tire cover. We'll just pull it out and set it aside for installation later.

Next, we need to remove the rear threshold. To remove the threshold, there are a total of four fasteners that we'll need to go ahead and remove. These just twist out like a screw. There's two on the passenger side and two on the driver's side where we can repeat the same process. Now once we remove those, we're going to go ahead and pull up and out on the threshold to release any fasteners underneath.

Now that our threshold is out of the way, we're next going to remove the fasteners and secure the carpeting behind the tail light assembly. We're going to go ahead and remove a couple of them. One here towards the back lid portion of the trunk, and one just out behind the seat. To remove the fasteners, we can use a flat blade screwdriver or, in this case, we're going to use an interior trim panel tool. We'll go ahead and pop them free, pull them out, and set them aside for reinstallation later. Now with those fasteners removed, we're going to go ahead and slide the carpeting out of our way.

Now with the carpeting out of the way, we'll go ahead and locate the manufacturer's wiring that comes out of the tail light. There's a connector here that we'll need to separate. To separate them, we can press on the locking tab and pull the two apart. Now once we have separated the two connectors, we'll go ahead and bring in our new wiring harness. This is our Two Ready Custom Fit Wiring Harness, the converter box, coming out of the converter box is going to be the yellow and brown wire T connector. The connectors here will match the manufacturer's wiring connectors, and we can plug directly into them. Now with that done, we also have a green wire T connector coming from our converter box, and this is going to route over the passenger side and repeat the same process. When routing over to the passenger side, we're just going to basically follow the manufacturer's wiring as it routes underneath the threshold that we removed earlier. Now once we've made our connection, we'll go ahead and use the zip ties provided to secure our wiring as necessary. Then once we have our wiring secured, we'll go ahead and take a pair of side cutters and just cut off the excess from the zip ties to clean up the install look, and get the excess out of the way. Now with our connections made here on the passenger side, we can go ahead and reinstall the carpeting. All right. Next we're going to take the converter box and mount it. To mount it, we're looking for a clean, flat surface, preferably sheet metal, to use the two-way adhesive provided with our install kit. Remove one side of the adhesive and attach it to the converter box, and the other side, and attach it to the body of the vehicle. Here below the driver's side tail light is a perfect location. Go ahead and firmly press it into place to get a good, cohesive connection. Next, we'll take the white wire with our preattached ring terminal. This is going to ground for the converter box and four-pole trailer connector. We're going to mount it here to the body or sheet metal of the vehicle. What we're looking for is an area where the sheet metal doubles up for a good, secured connection point. Next, we'll move to the red wire that comes from our converter box. This is our 12-volt power supply for our converter box, and ultimately gets connected to the battery. Now to connect the extra length of black wire with the red wire, we'll use the yellow butt connector provided with our install kit. Slide the butt connector on to the power wire and crimp it down. Then we'll slide it on to the red power wire and crimp it down. Go ahead and give the two wires a quick tug to make sure we got a good connection point, then I recommend to wrap it up with some black electrical tape to help keep it free from dirt, dust, debris, and moisture. All right. Next, we'll go ahead and start routing our power wire. Keep in mind, when routing your wire, to stay away from any moving component, so your steering or suspension, or excessive heat, such as exhaust. Now for routing our power wire, we recommend to go through one of the manufactured grommets. For this application, we can lift up the carpeting just behind the back seat and locate the manufacturer's grommet that we can route through. To route through it, we're just going to use our utility knife to cut a small slice in the grommet, and then push our wire through it. Now with the power wire, route it outside and underneath the vehicle, we're going to move back here behind the driver's side tail light assembly, secure the remaining pieces of our wiring, and then reinstall the vehicle's interior. Now we'll go ahead and move underneath the vehicle, grab hold of the power wire, and pull it through. Now once we get underneath the vehicle, to help stay away from the exhaust and suspension, we're just running over the top of the rear axle, and then following the manufacturer's brake lines up towards the engine compartment. Now to make it easier to follow the manufacturer's brake lines, we're going to remove the shield or cover underneath, route our wire, and then reinstall it. Keep in mind as we route our wire, we'll also use the zip ties to secure it as necessary. Once we get to the bottom of the engine compartment, we'll feed it up behind the sheet metal into the engine compartment, and ultimately to the top of the firewall. Now with our power wire routed into the engine compartment, go ahead and pull it up, and we need to route it over to the passenger side, where we can access the manufacturer's 12-volt battery source. To route over to the passenger side, we're going to move along the top trim here, and we'll use a small drill bit to drill into the plastic so we can create some attachment points for our zip tie to secure our wiring. Now to access the 12-volt battery supply, we're going to remove the fuse box cover here, and pull back on the cover latch block, and just lift it up and out of the way. Here, we have the battery supply coming in to the fuse box. We're going to use the post here to connect our inline fuse holder to. Our fuse holder is a loop that we're just going to cut in half. We'll strip back both sides and attach a ring terminal to one side for connecting to our battery source, and a butt connector to the other. Now with the fuse holder prepped, we can cut off the excess from our power wire, strip it back, and add it to the other side of our butt connector. Then we can wrap up our butt connector with some black electrical tape. Then we'll go ahead and install the ring terminal on to the battery terminal. To do that, we'll remove the nut and the positive battery post, install the ring terminal, and then resecure the nut. We can close the fuse box cover, we'll take the fuse holder, put our fuse in, and then finish securing the wiring. Go ahead and cut off the excess from the zip ties to clean up our install look. Now to test our 4-pole trailer connector, we'll simply take our test light, ground clamp, put it on the white wire terminal, and then test the brown wire terminal for our running light circuit. Then the next terminal over will be the yellow wire terminal for the driver side turn signal and brake. Our fourth pin will be the green wire terminal for the passenger side turn signal and brake. Just like that, it's installed and we're ready to hit the road. There you have it for the Two Ready T1 Vehicle Wiring Harness with 4-Pole Trailer Connector, part number 118487, on our 2015 Ford Mustang. .


Info for this part was:

Employee Joshua S
Video by:
Joshua S
Employee Michael B
Video by:
Michael B
Employee Nicholas E
Test Fit:
Nicholas E
Employee Shane H
Test Fit:
Shane H
Employee Jacob T
Video Edited:
Jacob T
Employee Cole B
Installed by:
Cole B

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