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Tekonsha T-One Vehicle Wiring Harness Installation - 2021 Jeep Grand Cherokee L

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How to Install the Tekonsha T-One Vehicle Wiring Harness on a 2021 Jeep Grand Cherokee L


Hi there, Jeep owners. Today on your 2021 Jeep Grand Cherokee L, we're gonna be taking a look at and showing you how to install Tekonsha's 4-pole flat trailer connector vehicle wiring harness. And this is what our wiring looks like when it's installed. It is a 4-pole flat trailer connection that lives outside the vehicle and has an integrated dust boot into it which you can use to secure it to your safety chain loop when not in use. When you do go to use it, though, you're gonna get all of your lighting signals out of your 4-pole flat trailer connector here. This includes your left turn signal, right turn signal, tail lamps and break lamps, which will keep you DOT-compliant in all states.

The thing that I really like about this harness though is that it has a module that's integrated into the harness, and that module is what actually produces the signals that come out of our 4 way here. The module ties into both your passenger and driver side taillight assemblies with custom-fit connectors that plug right inline in between the assembly and the factory connector on the vehicle. This allows the module to monitor all of those signals that's going to our tail light assembly and when it sees that, a signal whether it be a turn, stop, or tail light signal, the module goes, "Oh hey, we need this here for our trailer", it'll reproduce that signal and send it out the 4-pole. That's really nice because if you have any shorts on your trailer or issues, if it was tied right into your lights on your vehicle, it would cause an issue with both the trailer lights and your vehicle lights. But since the module here is taking care of your trailer, it's isolating it from the vehicle so if you have any fault on your trailer, the module would just shut down that circuit, or in the event that the module is unable to shut down the circuit in time, the module has its own dedicated power circuit with its own circuit protection so the fuse would just open for that circuit.

It wouldn't affect anything here on the vehicle so you could repair the issues with your trailer and then replace the fuse for your lighting here and then you'll be back up an running once again, so I love that it keeps our vehicle nice and safe while providing us with all those necessary lighting signals. If you didn't want to secure it to your hitch with the safety chain loop, we do have brackets available here at Etrailer and the straw type hitch is a great candidate for it, so we're gonna be talking to our customer here to see if they'd like to upgrade it to get one of those there as well. We'll begin our installation here at the back of the vehicle by removing both the driver and passenger side tail light assemblies. Our harness here's gonna plug inline between the connectors that plug into those assemblies, so that's gonna be our first step. So first we'll take out the cover here.

There's a single fastener right here. Its just push pin, so we can get a screwdriver behind that or trim panel tool and we can pop that pin out of there. I like to start with a screwdriver 'cause these can be pretty difficult to get behind, and then switch to a trim panel tool to get under it to get it pulled out of there. In some instances the head of these is so flimsy that your trim panel tool won't work, so you can use a pair of pliers instead. So, in that case, we'll just take our screwdriver, then we're gonna kinda flip this up and then we'll use a pair of needle nose pliers to get under the head.

Ensure that we can squeeze on the center piece there. And then we can pry this out of there. After we've got that removed, we can pull our panel off. Just kinda working it there, just running my finger down to snap the connections loose there and then pulling it away to get it off. Behind that there we're gonna have a single fastener here. It's a torx bit we're gonna need to remove that. We'll use a T30 torx bit to remove it. And now we can remove our tail light assembly. I like to use a trim panel tool to kind of give me some slight pressure rearward and then we're just kind of rocking it there a little bit. We got that to release and it looks like that the peg actually comes straight to the side so once we get it released here at the back, we're kind of pulling outward and rearward at the same time. It's almost like a 45 degree angle that you wanna pull away. We can then disconnect our electrical connector here, push the lock tab back out the way. Then we can press the release tab there and slide the connector off. We'll do the same thing over on the other side. So we got our assemblies out of the way. We're gonna now use a fish wire to get our wiring from down below pulled up behind our fascia here into this location so we can plug it into our connector here. We're gonna be using a piece of airline tubing, there's a good chance you don't have this at home, but something you do probably have at home and it works really well is a metal coat hanger. You could take that apart 'cause that way it's flexible, but rigid enough where you can push it through things, but also flex around some minor curves. So we're just gonna poke this down and we can see some day light as we kinda look down here. So we're just trying to look for that day light and get this to get all the way to the bottom. And sometimes when you're feeding this down, perhaps it may get caught up there towards the bottom of the fascia 'cause it does kinds curve in, so it's not uncommon that you have to take your hand and reach around the underside here and just feel around for it and there it is. I can feel it right there, it did get caught up on a little something here. So, we'll just grab this and then pull that down. So now that we've got it down here, we're gonna use some electrical tape to attach our wiring to it and pull it back up. This is our passenger side so that's gonna be the green wire off of our module, so we'll just take off that there, separate this out like this and our electrical tape here is just gonna wrap around the connector ends there so that way we can pull this up behind our assembly there. And then we're now just pulling this fish wire. Sometimes you gotta kinda jiggle it around to get our wiring pulled up behind our assembly here. We'll now detach it from our pull wire and we can plug our connectors in, let's take a look at this one here. This is this one so this will plug into this side over here. So we'll take our factory connector here and the other connector that matches up so this is gonna be the male side. It's gonna plug into the female side on our vehicle Just plug those together and then click that in place. We can now take the other side of our new harness here. This is gonna plug into our tail light assembly, so we'll just grab that. Plug this into the bottom there, and then we can put our tail light assembly back into place. What I do like to do though is I like to put a zip tie right here just to kinda put a little bit of a wire relief here on our connector. So I'm gonna grab a zip tie and put that on there real quick before I slide it all the way back in. Go ahead and snip our zip tie and then we can reinstall our tail light assemblies. Just snaps back into place and then we'll reinstall our fasteners. We're now underneath the vehicle. We took the double-sided adhesive that comes in our kit, stuck it onto the backside of the module and we peeled back the other side of the adhesive backing and then we're sticking it in place and we're just kinda sticking it right here to the side of our hitch that's on here. And then we're gonna, we took the yellow wire here and we're routing that across towards the other side. We're also gonna take our 4 way connector here and this is also gonna route, not all the way to the other side, but we're gonna route it towards the middle of the vehicle. So here you can see our hitch right there. That's where we want our wiring to run over to. There is a mounting bracket here, so if you wanted to get a 4-pole bracket, we sell those here at Etrailer, so you can mount it onto a bracket or you could just take the dust cap that it comes included with and just wrap that around your hitch. The excess wire that we've got here, we can bundle all that up and hide that back here behind our hitch. So we're just zip tying up that excess right there and our yellow wire continued on all the way to the driver's side. Went ahead and dropped down a pull wire just like we did on the driver's side, so now we're gonna tape our yellow wire to this so we can pull that up, but also while we're down here there's a couple more connections that we can go ahead and make, so before I do this, let's head back over to the module. We're gonna attach our ground wire here, which is the white wire with the ring terminal. We routed it over here towards the middle. There's a bolt right here we can actually remove and attach it to that. So we're just gonna zip this out. Slide our ring terminal over the bolt and then just reinstall the bolt. Now we'll extend our black wire coming off our module. That's our power wire. It is pre-stripped, but I like to strip just a little bit more back to make it easier to make our connection here. You're gonna also receive a large amount of excess black wire here. This is gonna route up towards the front of the vehicle so we can connect it to our battery to get power for our new harness here. So we're gonna go ahead and take one end of that harness, we're gonna strip it back and this is just gonna attach to the black wire there. So we're gonna use the heat shrink butt connector that comes in our kit, slide it over the wire, crimp her down, and then crimp the other side on to here. We'll then use our heat gun to shrink it down. So we're back up top again. We just used our fish wire to pull the yellow wire up, it plugs inline just like we did over on the passenger side. Zip tied up the excess to the factory wiring there to make sure it doesn't fall back down and touch our exhaust or anything. So we can go ahead and reinstall this assembly as well. So now we need to route our black wire up towards our engine compartment. To do this, we're in kind of a really poor spot here at the back because of where our exhaust is on each side, it kind of puts it at a risky location, so we went over here a little towards the middle so we could be on the other side of this heat shield here. We did drill a small hole through this plastic right here just so we could poke the wire through that to avoid staying, you know, getting to close to that exhaust there. From there we just follow along the inside of this panel. We do drill another whole here towards the other side. This way we're past our muffler and we're away from that heat. We come out the other side of it there and then go above our rear suspension here. We come out the other side of our rear suspension here and we go around the outside of our fuel tank. I'm gonna go ahead and put a zip tie on it right here to make sure that we stay towards this outside here. And then from here, we just go above this paneling that you can see right in front of me here. And there's plenty of room to just stick your arm up in there and push forward. What I did is I pushed it to this middle section here, I pulled it down, and then from here I pushed it back up right to the other side 'cause then you can reach right up here and grab your wire to continue pulling it on. And then we just continued pulling it all the way above this paneling until we come out right over here. From here, we do go behind the heat shield here to again protect it from the exhaust and it comes out the other side of our heat shield right up here. Before routing the wire, I did take the fish wire that we've been using, and I also poked that down from our engine compartment down to this location. So now I can take the rest of my black wire that we've got routed here, we'll tape it to this and pull it up just like we we're doing at the back. So here we are again back up top on our engine compartment. Pull on that pull wire to get our wire all the way pulled up. After you pull it up too, it is a good idea to really quick, just take a look underneath and make sure that the wire is all the way pulled up. Every now and then you could have a loop that catches around a head of a little stud or something like that. You don't have it pulled all the way up and we don't want anything dragging or hanging loose down there. After you've ensured that you do have it pulled all the way up, we're just gonna be routing it towards our fuse box up here. We lift up on our fuse box lid, just pressing on both those release tabs there. They have little lock pictures next to them. We can move that out of the way and we'll attach it to the post here for our battery right there. We're gonna choose this location because this is where it shows us is our positive and where we would jump start the vehicle if we had to jump it or anything, so we know this is a direct connection back to battery. So now that we've got our wire routed up here, we're gonna go ahead and trim it to length. We'll then strip back our wiring here and we can attach another heat shrink butt connector to the end of this wire here. And on the other side we're gonna attach the fuse harness that comes in our kit. This does come looped. I've already cut it in half and stripped back each end, so you can do that as well and this just pokes in here. Crimp it down, and on the other side of our fuse harness we're gonna put a ring terminal so that way we can attach it to that stud to get our positive so it just slides over it, crimps right into place. We'll now take our heat gun and we'll shrink down our butt connector here to seal this up to ensure a long lasting connection. We'll now take a 13 millimeter socket to remove the nut. Take the ring terminal that comes in our kit. We're just gonna slide this right on over the stud and then reinstall our nut. At this point now, we've got all of our connections made. So we can go ahead and install the fuse as well that comes in our kit so we're just gonna open up our fuse harness there, take the fuse that comes in the kit, slide it down into the harness, close it up, and we're ready to now test out our new wiring. I'm gonna go ahead and put the put lid back on as well just to see if we need to make any modifications. I don't believe we will because of the way this rolls down like that. Our wires should kinda just want to sit off to the side there like that, and it does. So now we've gone ahead and plugged in the tester here at the back of the vehicle so we can verify that our wiring's working properly. You can use your trailer at home, but I highly recommend that you use a tester like this in case you have any faults or shorts on your trailer, you can get some false readings and you might think it's an issue with your vehicle, but it's your trailer the whole time. A tester like this will help you ensure that your vehicle is working properly. You can get these here at Etrailer, and we're gonna operate our lighting signals starting with our left turn signal, right turn signal, tail lamps, and brake lamps. With all of our signals working properly, we're ready to load up our trailer and hit the road. And that completes our installation of Tekonsha's 4-pole flat trailer connector vehicle wiring harness on our 2021 Jeep Grand Cherokee L..


Info for this part was:

Employee Jeff D
Installed by:
Jeff D
Employee Joshua S
Video Edited:
Joshua S
Employee Jacob T
Video Edited:
Jacob T
Employee Dustin K
Video by:
Dustin K
Employee Jonathan Y
Video by:
Jonathan Y
Employee Conner L
Test Fit:
Conner L
Employee David F
Test Fit:
David F
Employee Ryan G
Test Fit:
Ryan G

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