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Trailer Wiring Harness Installation - 2008 Toyota Highlander

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How to Install a Wiring Harness for a Trailer on a 2008 Toyota Highlander

Today on this 2008 Toyota Highlander we will be installing the wiring harness part number 118449. The first thing I want to point out with this wiring harness before we get started is that it does come in two pieces. The larger piece with the larger 10 pin port is going to plug in underneath the dash on the interior of the vehicle. The second part which contains our 4-pole end is going to plug in at the rear back in our cargo area. We are going to start off by plugging the larger section in underneath the dash first. The port underneath the dash is located just left of the brake pedal attached to the main wiring harness lead right there. Now that we have the port located we can plug our harness in line and then we want to take the modulite box and we need to adhere it to a surface underneath the dash. We have got double sided tape on the back side so we can just peel that away and just find a place to adhere it. 00:54

There is actually a silver diagnostic box that provides a nice flat surface for us to adhere it to. With our modulite box adhered we just want to zip tie up any loose wires that you have underneath there and then we will go back to the cargo area and attach the second half of the wiring harness. Now we are in the rear cargo section of the vehicle and the connection point for our second section of our wiring harness is located on the driver side underneath the storage compartment. We are going to need to remove some of the flooring pieces to gain access to that. Start with the rear lid and then the cover for the side compartment as well. What we are needing to remove is this whole storage compartment. There is a push pin here holding it in to place and two screws at the bottom. Now we can remove the compartment. We are going to need to manipulate it around this section to get it out. You want to be careful and make sure you do not damage anything when doing so. 01:55

With that storage compartment removed you can see right here our 4-pin connector is located right here. We just want to take the other half of our wiring harness and plug that in. We can reinstall the storage container and then the remaining covers in the inside of the vehicle. With our 4-pole plugged in we can either do one of two things. The instructions state to leave the 4-pole mounted inside the vehicle which is what we recommend unless you need a 6 or 7-pole plug on your vehicle in which case you will need to route it underneath the vehicle. Finally we need to go up underneath the hood compartment and put in the final fuse to activate our tow package. The fuse block that we are looking for is just to the right of the battery right here. Remove the lid and we want to locate the fuse that is specified for the towing package which is right here. They do label it as a 30 amp fuse however our wiring harness only requires a 10 amp fuse to activate it. We are going to take the 10 amp fuse provided with the installation kit and plug that in line. With that fuse installed our installation is complete. That will conclude the installation of wiring harness part number 118449 on a 2008 Toyota Highlander.



After installing how do you plug into the trailer?

Etrailer Expert

Rachael H.


The 4-way flat portion will be routed outside the vehicle and will plug into the trailer side connector. I realize this video did not show that final step of the installation but I have provided a link to another one of our videos that shows the installer testing the side connector that would plug into the trailer wiring harness at about 6 minute and 35 seconds of the video.

Info for this part was:

Employee Zack K
Video Edited:
Zack K
Employee Andrew K
Video Edited:
Andrew K
Employee Joshua S
Video Edited:
Joshua S
Employee Jacob T
Video Edited:
Jacob T
Employee Chris R
Video Edited:
Chris R
Employee Jeff D
Installed by:
Jeff D
Employee Cole B
Installed by:
Cole B
Employee Nicholas E
Test Fit:
Nicholas E
Employee Randy B
Test Fit:
Randy B
Employee Brent H
Test Fit:
Brent H
Employee Shane H
Test Fit:
Shane H
Employee Robert C
Test Fit:
Robert C
Employee Andrew L
Video by:
Andrew L
Employee Kathleen M
Video by:
Kathleen M
Employee Jonathan Y
Video by:
Jonathan Y
Employee Michael B
Video by:
Michael B

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