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Trailer Wiring Harness Installation - 2012 Toyota Highlander

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How to Install a Trailer Wiring Harness on a 2012 Toyota Highlander

Today on our 2012 Toyota Highlander, we'll be installing the Tow Ready T1 connector, part number 118449. Our first step is going to be installing the converter box on the driver's side up underneath the dash. You'll locate the manufacturer's 10-pin plug which identically matched the Tow Ready plug that goes to our converter box and plug into the manufacturer's plug. Next, we'll go ahead and peel back the two-way adhesive when we mount our converter box. We'll be mounting to a clean flat piece of sheet metal. You look up underneath the dash on the driver's side, you can locate a flat area to attach to.

Next, we'll go ahead and use a couple of the black zip ties provided with our install kit and secure up the wiring. That will complete installing the converter box. Next, we'll move to the rear tail gate of the vehicle and open it up. We'll need to remove the interior trim components to access the manufacturer's plug to plug in our 4-pole connector. And now, we'll need to remove the cargo tray on the driver's side.

There are three fasteners securing it that will need to be removed first. Now, we can go ahead and gently pry it out in position and remove it. This will open up so we can plug in to the manufacturer's white connector, you can now see with the cargo tray removed. We'll go ahead and plug the 4-pole connector into it now, and then we can go ahead and remove the grommet or plug to route our 4-pole connector outside the vehicle. To do this, we'll remove the grommet or plug, cut a slice in it using our side cutters, then go ahead and feed the 4-pole connector outside the vehicle and reinstall the plug.

Now, we can go ahead and reinstall the interior trim components. With that done, we can get up underneath the vehicle, use a couple of the black zip ties, and secure our 4-pole connector to the hitch. Toward the final step, we'll be underneath the hood of the vehicle. We'll go ahead and remove the cover on the fuse box, insert the red 10-amp fuse provided with our install kit into the manufacturer's towing outlet. With that done, we'll go ahead and reinstall the fuse cover, close the hood, and that will complete the install of our Tow Ready T1 Connector, part number 118449 on our 2012 Toyota Highlander..

Philip S.


Recently purchased 2012 Highlander with trailer harness included. Trailer lights work on Right side, but we are not getting any current in the yellow wire no signals or brake light on the left side of trailer. The harness is good , all wires checkout, but no yellow current from Manufacturer's 4 prong outlet. How do I fix this?

Etrailer Expert

Jon G.


Try checking your owner's manual for any fuses or relays that are dedicated to the left turn/stop circuit. I tried looking it up online but I only found one fuse that was for all of the trailer light functions and that wouldn't be the problem if all of your other trailer light functions are working. Aside from that you would need to trace that wire as best you can to see if there are any places where the wire got damaged. Worst case scenario you'd need to bypass the OEM wiring (since you aren't getting signal on the OEM connector) with an aftermarket option that would splice in like the Tekonsha # 119147KIT.

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