Trailer Wiring Harness Installation - 2011 BMW X3

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How to Install a Trailer Wiring Harness on a 2011 BMW X3


Today on our 2011 BMW X-3, we're going to be taking a look at and installing the Curt Powered Tail Light Converter with 4-Pole Flat Trailer Connector, part number C59236. Here's what it's going to look like once it's installed on the vehicle. This is the dust cap that comes with it. It's just tied to our safety chain connection loop right there. You can also get brackets if you want to mount it outside the vehicle where it's a little bit easier and more permanently mounted, but this is going to do a great job of giving us 4-pole power here for a trailer or a cargo carrier. This kit is going to tap directly into the lines, so you'll have to splice it into the lines and you will have to identify what type of wiring system your car has on it for the lighting, but the instructions will help you do that. This comes with a heavy duty converter box that's going to make sure that you've got plenty of power and it's going to go directly to the battery with a power wire, so that it pulls 12 volts directly from there.

That way it's not putting as much of a strain on the vehicles wiring harness. That module box is also going to help protect the vehicle from any surges or shorts in the trailer. It's going to provide five amps on the turn and brake circuits and it's going to provide 7.5 amps on the tail light circuit, so it should give you plenty of power for the lighting on anything that you'll have behind it. Now, let's show you how to install it. The first thing we need to do to begin our installation is we will need to gain access to our tail lights in order to determine what type of lighting system it is, so that way we'll know how we'll need to hook up our wiring. You can follow the instructions in order to identify your lighting system. What we will need to do is we will need to start by popping this black cover off.

You just pry inwards on it. It'll come loose and you can set that aside. Then we will remove the 10 millimeter nuts that hold our tail light in place. Then we'll do that same thing for the other side. Here on the drivers side in order to remove the tail light, we'll grab onto it and gently pull straight towards the rear of the vehicle. Just slide it off of those studs and the light will come right out.

Then we'll take our connector and we'll push that tab down that's on the top and pull that connector right off. We'll do that same thing on the other side. Now with our connector we can begin testing to see which wires have power for all of our different circuits, but before we do that you will want to be sure to check and make sure that none of them have power when everything is off. None of them have power, now we can begin running our lights in order to test and check to see which ones have power for each circuit. First, we'll do the running lights, so it's going to be on that pin, which is going to be our yellow and black wire. Then next we'll do the turn signal, so it's going to be on that second pin in from the right, which is going to be the blue and green wire. Then finally the brake lights.

That's going to be this far pin over here, which is going to be our yellow and blue wire. Now here on the passenger side, we'll test it the same way we did on the drivers side in order to find which of these is our turn signal circuit. Now I'll take a piece of old airline tubing to use as a fish wire to help fish my wires from underneath, up through the opening in the tail light here. Now in order to give myself a little bit more room to work and make it easier to see, I'm going to lower the exhaust down. It's got some rubber isolators. It's got two that are here on the muffler and then one just in front of the rear axle that we're going to take down. Now it is a good idea to put up a support strap, so that way your exhaust cannot hang too low and possibly damage the component. I used some spray lube to help make removal of the rubber isolators a little bit easier. You can use a pry bar. Once we've got them lose, we can lower our support strap a little bit, so that way we've got some extra room to work now. I take the brown, white, yellow and red wires to my fish wire in order to pull them through up to the drivers side tail light housing. Before pulling that fish wire up through, I want to be sure that I can make the connection to this black power wire that's coming off the module box. I will use a butt connector that comes with the kit, slide it on and crimp that down. Then the other side of that, I'll need to take my length of black wire that comes with the kit, strip one end back, then I can install that. Then the other side of that yellow butt connector. I'll wrap that up with some black electrical tape. Now we'll pull our wiring up through. You want to do it gently just in case anything catches. Here's the box that we're going to be mounting to the body here inside the fascia and we're going to mount it as high up as we can so that we've got plenty of wire to work with up at the tail light. I've got a cloth with some rubbing alcohol. I'll clean both the back side of the box and I'll clean the area up high where I'm going to mount it. I'll take my double sided sticky tape and I've peeled one side off in order to stick it on the back of the box. Then you can peel the other side off and then we'll stick it up into the location. Before making any connections or anything like that, we'll need to be sure to locate the battery and disconnect the negative terminal. In this vehicle it's going to be underneath the rear cargo area. We will lift up our cover and move that out of the way. You'll need a flat head screwdriver for these two pins. YOu'll just need to rotate those 1/4 turn in order to loosen them. Once those are lose you can lift this panel up and now you've got access to your battery. We'll need a 10 millimeter socket in order to disconnect our negative cable. I have gone ahead and routed all the wires to their locations. We'll start with routing the green wire to the passenger side tail light. You run it over the frame bracket for the bumper rail, across the top and run it over the bumper rail bracket on the other side and up towards the tail light housing. I used a fish wire the same way I did in order to pull the wires up on the drivers side. Next I routed the 4-pole wire, routed it down along the hitch and then brought it down to my safety chain connection point and I used the dust cover to secure it to that connection point. From the black power wire, coming from the module I brought that down and just underneath the hitch here and then in that grommet that is right there in order to go in towards the battery. Now we'll reinstall our exhaust. Now we'll begin making all of our connections to the wiring that's behind the tail lights. The first one we'll do is the red wire and we're going to be connecting that to our brake light signal, which if you remember is the yellow and blue wire that's here on the end. We will clip that wire and strip both ends back, then we'll strip the end of our red wire back and then the end of the factory wiring coming from inside the vehicle. We'll twist that together with our red wire and then slide on one of our butt connectors and then we'll crimp down our connector. It's not a bad idea to pick up a pack of Deca heat shrink butt connectors. The 10 or 12 gauge rating that are yellow. They come in a pack of five. You can get those on our site, part number DW05745-5. We're going to use those to replace the Quickie connectors. For the other end, we'll insert our second wire and crimp that down. Then we'll do that same thing with our brown wire and with the yellow and black wire, that's our tail light signal. Then repeating that same process for the blue and green wire to connect it to our yellow wire for the turn signals. Then I'll use the heat gun. You can use other heat sources, but you want to be sure that if it has an open flame that you're not really getting that flame directly on these connectors. I'll use the self-tapping screw that comes with the kit in order to ground the system with the eyelet that's on the end of this white wire. Now you will want to be sure that wherever you decide to ground yours at, that there's nothing behind there that's going to possibly be damages like wiring or any other connections. Now, we can reinstall our tail light. Now I will take our green wire and we'll connect it just like we did on the other side and after testing we found that on this side, the turn signal is going to be the blue with brown wire. We're going to connect that the same way we did on the other side. Now for our power wire, we're going to connect it to the stud that's down here on the floor on the other side of the battery, because it's got this large cable that connects directly to the positive terminal. We will want to get our approximate amount of wire that we'll need to run this around the battery, but then also leaving a small gap before we get to that so that we can install our in-line fuse holder. Now we will cut that wire about the length that we need and then we'll make sure to have this routed and secured, so it's out of the way of all the other wires around the battery. Now we'll strip the end of that back and put it into the end with one of our yellow butt connectors that comes with the kit and crimp it down. Then we'll take our in-line fuse holder and I'm going to cut it a little bit off center and then I'll strip both ends of that back. One end I'll install into the other side of that butt connector and on the other end I'll put the ring terminal that comes with the kit onto the wire. I'll take a 13 millimeter socket and remove the nut that's on the top of that stud. I'll slide that ring terminal over that stud and reinstall the nut. Once I've got that connected, I'm ready to install my fuse. Get that inserted all the way down into the fuse holder and put that dust cap over the top. Now with all that hooked up, we're ready to reinstall the negative terminal onto our battery. Now we can reinstall the cargo floor. Now that we've got it installed, let's test it and make sure it's working properly. We're going to use part number I26 in order to do that, so first we'll check our tail lights, they're working. Left turn signal, right turn signal and brake lights. Everything is working as it should. That's going to complete our look at and installation of the Curt Powered Tail Light Converter with 4-Pole Flat Trailer Connector, part number C59236 on our 2011 BMW X-3.


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