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Trailer Wiring Harness Installation - 1999 Lexus RX 300

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How to Install a Wiring Harness for a Trailer on a 1999 Lexus RX 300

Today we are going to show you how to do a hardwire install on a 1999 Lexus RX300. We will be installing part number 118176. We will also be using the accompanying Modulite wiring kit part number 118151. To begin our install what we are going to do is take apart the plastic on the inside of the vehicle. It is pretty time consuming but it is very easy to do if you just take your time. So we will open up the trunk and get inside. We start by taking apart the trunk liner and getting down to where the spare tire is. Also take out the side pockets there is one on each side. We are going to use that for access so that it can fit into our wiring harness. We will have to take off our tail lights to test and see what wire does what. Now we still have to take these 2 pockets out to get to our wiring harness and make it a little easier to get too.

These simply pop out just take a screw driver and with one end there is a little pocket and pry them out like so. As you can see our wiring harness goes back up in here there is going to be one on each side. What we need to do is get behind this panel and pull it loose. First we have to take this threshold cover off. Then we can get to the harness after removing this tie down piece. There are 1 them on both sides of the vehicle. Next what we want to do is unbolt our light here. Not to mention there are a few covers you might have to pop off first to gain access to the bolts. Take this bolt and the other out and the light simply pops out. There is a little rubber grommet in here that you want to pull out. We pull it out so we can put little slice in it to run a wire through it. We have sliced our grommet here and need to run the wires through. When we are finished we will button all of this back together and push this grommet back into place.

What we need to do next is make a ground connection attach it to the body work right here. Now we will expose this wiring here so we have more working room so we can make our splices. With our running lights on we can see what bulb it is going too. So we know it is going to one of these wires here. We can eliminated these to the left and test one of the green wires on the right. Luckily we got it right on the first try so we can go ahead and make our splice there and get our circuit out of the way. We will do the same thing for the left turn signal. There are 2 white wires so chances are they will both be ground making it very likely that the green wire is the turn signal so we will make that connection. The last thing we need to work on is our stop light circuit. It is probably this one right here but it is still always good to have someone step on the brake on the other side. Now we can just tape all of this back up and reassemble it. Running the green wire all the way across and basically the same thing on the passenger side. However sometimes the wire is on the short side so what we will do is go ahead and splice this and add an extension. So we do not have to have a bow string going all the way across. Since we have already done the other side we know that the green wires are the wires to splice into and make a connection with. Next thing we need to do is run our power wire to the battery. What we are going to do is run it through here make another splice and follow the frame rail out to the battery.

Go ahead and pull out our wiring harness to get it out of the way. What is going to happen is it is going to come up and around this edge and fall back into the bucket here. So when we are not using it we can store it inside of there. At this point you can go ahead and start reassembling your interior now. What we are going to do next is start fishing our wire towards the front. The farther you go the less attachment points or things for it to be threaded through. As long as you keep your line tight and away from the exhaust you should be okay. We also want a little bit of slack so we can zip tie it off. Make sure it is not going to hit anything that moves like these control arms here or even your axle. Then lets follow this parking brake line just a little further up and then zip tie some of this stuff up now. Drag it down all the way to this nylon support here and make it tight inside of that. You also do not want it to close to your muffler. Make sure you have plenty of clearance. We will also thread through this body mount right here. Then we will start threading it straight up and along the firewall. Behind the steering components. We are just going to put this here for now and then reach down and pull this all up. We got our wire run down through our firewall make sure we tucked it down behind the tubes and everything. Again make sure it is away from the steering components. We will go ahead and tie it down to this port right here. Then go back and tuck this wire down by the box here and go underneath.

Next we will make our battery connections loose and install our hot lead. We will install our fuse holder next. Start off by cutting it in half and putting your ends on. Go ahead and reconnect it to the battery. Then install the fuses and then reconnect the negative battery cable. With our install complete we tested it and it works just fine. It is time to show you how to use it, basically you just pull out as much as you need it. Just keep the harness away from the latch of the trunk. You do not want the harness anywhere near that. Go ahead and shut your door and as you can see you still have some more harness you can pull out if needed. At that point you can hook up your trailer and your good to go. If your not using it instead of your harness hanging out and dragging or getting all messed up you can put it back inside the compartment in the vehicle. That completes the install of part number 118176. Also the wiring installation kit part number 118151. Both installed on a 1999 Lexus RX3000.

Info for this part was:

Employee Zack K
Video Edited:
Zack K
Employee Joshua S
Video Edited:
Joshua S
Employee Jacob T
Video Edited:
Jacob T
Employee Andrew K
Video by:
Andrew K
Employee Dustin K
Video by:
Dustin K
Employee Nicholas E
Test Fit:
Nicholas E
Employee David F
Test Fit:
David F
Employee Cole B
Installed by:
Cole B

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