Troubleshooting 4-Pole Factory Wiring Harness on 2008 Toyota Highlander

Updated 10/14/2014 | Published 10/13/2014

Question:

I have attached the pics of my system. It already has a tow-package installed, I thought, but I do not believe that it has a converter. the left light on a trailer stays on all the time. No turn signal, No brake. On all the time on the left side. Please advise, as I already have the flat 4 to square 4 connector on the vehicle. Thank you.

asked by: Wiley W

Expert Reply:

If your trailer lights just recently started malfunctioning, I recommend that you start by checking to make sure that you don't have a blown fuse or a bad relay in your 2008 Toyota Highlander. You will want to check all of the fuses and relays that relate to the tow package.

If all fuses and relays check out to be fine, I would then check the grounds on both the Highlander and your trailer. You will want to check to make sure that the ground wire is secured tightly to a clean metal surface that is free of dirt and corrosion. Each tail light assembly at the back of the trailer must also have a ground. These are most commonly grounded to the trailer frame or through the bolts of the tail lamp assembly.

If you find that all of the grounds check out to be fine and the lights on your trailer still aren't functioning properly, please feel free to email me and I would be happy to provide you with additional suggestions to try and locate the issue.

I have also attached a help article which covers some additional troubleshooting steps for wiring installations that you may want to take a look at.

expert reply by: Leah S