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Trailer Wiring Harness Installation - 2015 Ford Transit T250

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How to Install a Trailer Wiring Harness on a 2015 Ford Transit T250

Today on our 2015 Ford Transit T250, we're going to be installing the Tow Ready T-One Vehicle Wiring Harness with the 4-Pole Flat Trailer Connector. Part number is 118643. We've got your wiring harness laid out the way it's going to go in the vehicle. The yellow and brown wire comes over and it's going to be connected behind the driver's side taillight. The green wire comes over, it's going to be connected behind the passenger's side taillight. This is, of course, what the main goal is, is to get our 4-pole flat wire to the back of the vehicle so we can hook up our trailer.

You got your small module box. That's powered by a 12 volt power wire. Your kit's going to have the wire that we need to get up to the front of the vehicle and make the connection to the battery, as well as all the hardware and the fuse holders that we need to make those connections and finally, we've got our small, white ground wire here. This gets grounded to the body of the vehicle to complete our circuit and provide power here to the rear. We going to have 2 torx bits that are going to be located on each of our taillight housings here. We're going to want to remove those.

That's going to be just a standard torx bit. It's a T25. They work just like a screw would. Now we're going to go to the passenger's side and we've got 2 more screws located in that same location that we'll remove. Now we're going to take a small wedge, you can use a screwdriver if you like, kind of wrap it with some towels, and we just want to put it in between the body and the taillight and try to separate the pressure clips that are holding the housing in.

You can see here on the back side we've got 1 connector that's holding the housing to the vehicle, so we're going to separate that. Once we have these separated, we're going to set the housings in a safe place. It doesn't say to do this in the instructions, but to help us in routing our wires we need to go right through this little area right here. We're going to take these 2 torx screws out here as well, just to give us a little extra room to work. They're the same size as the ones that held the taillight in, so it will be a T25. We'll do this on both sides, just like the taillights.

You can see that's going to give us just a little bit of room to kind of flex that out and help get our connectors down and through. Here on the driver's side, we're going to connect the smaller portion of our new T-One connector right into our factory plug. You'll want to listen for a click and then give it a pull, make sure that's a nice, strong connection. Then we're going to feed through our 4-pole wire and also our green wire right down and through this opening here and then we'll also run the 4-pole wire back through that same little gap. Then let's guide them right down through this slot. Then we can just reach up from the bottom and pull the slack on through. That's just going to leave us with our black 12 volt power wire and our white ground wire over here that we need to connect, with the exception of course of plugging that into the back of our taillight. Next up is going to be to find a suitable mounting location. You'll want to find a spot, put your taillight up there, make sure it's going to work. This spot looked like it would work really well when we mocked up our taillight, so what we'll do is clean off the back of the module and also the mounting location with some alcohol. Now let's take the double-sided, foam tape and place it right on the back of the module. Press down firmly. You really want to make sure you get that stuck on there good. We also need to ground our white wire out to the surface of our body. As you can see, there's a small tab there that allows you to put a self-tapping screw in there for a little bit of additional security, so we're going to put our white wire right behind that so we'll be taking care of 2 jobs with 1 hole. We'll just mock up where we want that module to go and let's just make a little mark there. We're going to use a 3/32nds drill bit just to drill a small pilot hole. You want to check behind to make sure you don't have any wiring or anything there that you might hit. Then we can pull off that double-sided tape and reattach it. Just like before, we want to really push down firmly. Make sure that gets a good hold. Of course, that self-tapper is probably going to give us all the support we need, but just make sure. Now we'll have 1 final connection to make here. That's going to be our black 12 volt power wire. We'll take the length of wire that we've got, roll off a little bit of it here, and this time instead of trying to feed everything down and through, we just going to pass this up from the bottom, see if we can't get a hold of it up here in our corner. With that up and through, let's strip the end off of it. We're going to connect the provided butt connector to our 12 volt power side coming out of the module. Make sure that's good and secure and then we'll strip the wire we just ran up and through and we'll add that into the other side of that connector. Give it a pull. Make sure it's nice and tight, then we'll just wrap it up with a little tape, a little extra security. Now I'm just going to tidy up the wire a little bit. You can see we've got our green wire, our black wire, and our 4-pole wire that are going to run down through there. We're just going to put a little piece of wire loom on there to clean up that look. We'll just add that right around that wiring, maybe put just a little piece of tape around the end of it here to hold it in place. As you can see there, that really cleans up that look and gives us a nice finish. Now that we've got everything over here ran, let's just put our screws back in that we're holding bumper cover in place. Remember we took 2 out so we're going to put 2 back in. With those nice and secure, let's get our taillight housing. We'll go right back into that factory plug with our new wiring harness and slide our taillight housing right back into place. Once that's clicked in we'll replace the 2 screws that hold it in place. You can see we've got really nice, clean look. The only thing that you're going to be able to see that's any different than it was before is that we've now got just that little piece of wire loom running down, so it's a really nice, clean look. You can see our 12 volt power wire here under the vehicle. We're just going to set that up and out of the way for now. That's going to be one of the last things that we'll deal with. The next step, we're going to run our 4-pole wire up and over the rear part of the frame, as well as our green wire. You can see our 4-pole that's going to wind up here, so we'll let that be and we'll continue with the green wire over to the passenger's side. Underneath the bumper here there's not a lot of stuff to tuck it into, but we do have holes across every bumper support that we'll be able to use zip ties and secure it to. Now let's guide the end of our green wire right up in that same slot. Then we'll just pull that slack, because you can see we've got quite a bit of slack here, we're going to pull that. We'll zip tie everything off and then we'll be able to hide this right in that little pocket. I'm going to start working from the driver's side over to the passenger's side. We're going to use the zip ties that we're provided. We'll go right through these bumper supports. They've got holes in them. It's like they we're designed for us to use specifically for this so that's awesome. This is where their journey together is going to end. We're going to keep going with the green wire. We're going to let the 4-pole hang out right down here. What we'll do is just bring it around and, as you can see, that protective cover does a nice job of holding it up and out of the way. We'll just finish securing our green wire on over. We've got that nice and secured. It's going to be up and out of the way. Let's take just a second to clean up any ends of our zip ties and let's head up top and connect that taillight. Now let's run our connector right up through the little slot. The smaller end is going to plugged into the factory harness just like we did on the driver's side, making sure you hear an audible click and that you can't pull it back apart. We've got our taillight housing we'll be connecting it to, but before we do that, I want to clean up this excess wire. We're just going to wrap up the excess that we have here and I'm going to zip tie it together. That will be then tucked away and forgotten about forever. I've got a little piece of 1/4" loom now that we're going to use, just like we did on the other side. We're just dealing with less wire, so we're using less loom and just like the other side, a little bit of tape will help hold it in place. Now the taillight assembly. Guide it into place, make our connection and we'll align the locking tabs here on the outside, push in until you hear those click, and then resecure with our 2 fasteners. Remember the 2 in the bumper we took out We're going to put those in as well and then we'll tighten all 4 of them down. Now it's time to run this 12 volt power up to our 12 volt power source in the front of the vehicle. I'm going to use a little piece of airline tubing. You could use a little piece of stiff wire. As open as what it is underneath here, you might not even need a guide, but we're going to use it just in case. As we route this, we want to stay away from any sharp edges, any moving parts, any pinch points, anything that will cause damage to our wire. I'm going to just slowly guide it up towards the front. As you can see, our 12 volt power wire, we've run it up right across the hitch rail, right up to our little brake line connections. You just zip tie it off anywhere you've got any slack and then was really nice to run right up through. There's a small hole at each of these cross braces and we ran it right down through there, just stayed with it. We went through an open piece of steel here. Put a small piece of wire loom on there to protect it and then just stayed running through those channel openings until we got right up here to the back side of the subframe or just above where the subframe connects in, went right in the hole there, right out the larger hole here on the side, and then, after tucking it over this larger wire, I zip tied it right here just to help hold that slack, and then we went right up into the engine compartment. Now we're going to remove the negative battery terminal. To do that, you'll have to move the driver's seat all the way up. There is going to be a little panel here to kind of pop off. We'll use a 10 mm socket and we're going to remove the nut that's holding the cable onto the battery. Let me just lift that up and off and that wire is actually going to do a good job of holding it up so it doesn't make contact. Here's our fish wire. We just kind of stuck it up underneath our vehicle after we got done running it to the front. Now let's pull our tape off and we'll separate it from that pull. Now we're going to take our fuse holder and we're going to cut it about a 60/40 split. We'll need to strip both ends. Then we'll strip off the end of our black 12 volt wire and we're going to add a butt connector onto that, crimp that down, and then we're also going to crimp down the side after we add the fuse holder in. Now we're just going to wrap our connection up with a little bit of tape. You see we've got a little bit of excess wire here. We're going to tidy that up after we make our connections. The next step we're going to do is open the red cap and if you look down through, there's a couple holes there that come out here at the bottom. I'm going to take that wire and stick it right up through 1 of those holes. I'm going to add my ring terminal right to the end of that. With that on nice and secure, let's pull the nut off of our positive stud. With that off, we'll just slide that down, put just a little bend in the ring terminal and that will slide right down on our stud and we'll just tighten our nut back down. Now I'm going to put my finger in there and I'm going to hold that ring terminal, because when you get to that final tightening process right here, sometimes it wants to spin, so you just hold it in place. As you can see, we close our cover up there and we can't see that connection at all. Just got this little bit of excess here that we'll tidy up. Let's trim the end of those off. As you can see, if we ever need to make any kind of repairs we'll have plenty, but it's also tucked down out of the way so it's not very visible in normal, every day to day use. Now let's take our 15 amp fuse, slide that into the fuse holder, put the cap back on that, and now there is a small hole here. Some people will use that to zip tie the fuse holder to something to keep it up and to keep it visible. Some people will go through that hole and around the cap to keep it closed. Really a personal preference deal. Doesn't matter too much one way or another. We're just going to use ours, go right around these 2 tubes here. Everything is done here. Let's go reconnect our negative terminal and test our wiring. Now we're going to run through a test just to make sure we're getting all the signals back here that we need. Our test light, we're going to connect that onto our white wire. That's going to make sure that we've got a good ground and then we'll have somebody turn on the parking lights for us. That should give us a constant signal coming from this brown wire. Perfect. Now, let's have the left blinker turned on. That should be an intermittent signal from the yellow wire. Now we'll go to the right blinker. We should have that same thing, but this time from our green wire. Now we'll test the brakes. That should give us a constant signal from both the green and the yellow. Everything checks out great. We've done our job the right way and we're ready to head down the road. With everything working as it should, that's going to complete today's installation of the Tow Ready T-One Vehicle Wiring Harness, part number 118643, on our 2015 Ford Transit T250. .

Questions and Comments about this Video

Bill T.

Excellent video. Very well done. The technician is very professional. Very good job and very clear to understand. I was an automotive technician for 25 years and heavy equipment technician for 20 years. Retired 7 years ago. I really enjoy watching someone who knows what they are doing and enjoys their work.

Etrailer Expert
Reply from Jon G.

Thank you so much for the kind words!

Dave H.

Freakin Awesome video. The installer has the perfect voice, easy to hear and understand for this old guy. Video was super detailed and made following directions simple.Thank you for a great production on this install.

Etrailer Expert
Reply from Chris R.

Thanks so much for the kind words! I'll be sure to pass them along to Randy (the perfect voice).

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