Trailer Left Turn Signal Not Working with Curt Wiring Harness Installed on a 2008 Toyota Highlander

Updated 07/19/2016 | Published 07/18/2016

Products Featured in This Question

Curt T-Connector Vehicle Wiring Harness with 4-Pole Flat Trailer Connector

(1152)

$45.90

Hook Probe Circuit Tester

(66)

$14.40

Question:

My car is not supplying the correct signal to my trailer for the left turn signal. I know it is the car since I have a 12V supply that I can connect to the trailer and test all the light on the trailer and they all work fine. Also, on the car trailer connector, I swapped the right and left blinker lights, so if I use my right blinker the left blinker on the trailer goes on ... and it follows the left blinker car wire. Another factor that makes me think the issue is on the car. Also, I measure the voltage when the left blinker is on and it is 0V. Where can I check for grounding problems on the car? Can grounding cause just 1 wire to have issues? Also, are there separate fuses or relays that could be having issues that would only impact the left yellow wire? Is there any way to test out the power converter? On a side note, I purchased a Curt tow tester and the only LED that lights on that is the right blinker. But on my trailer and using a meter, I can see the other wires work. I found out I got a bad tow tester ... but that is a different issue/

asked by: Craig P

Expert Reply:

I tried to find an online copy of the owner's manual for the 2008 Toyota Highlander but it was not available. Check your owner's manual to find the fuse locations to determine if there is one for trailer left turn signal/brake lights.

If it is not a fuse, then there is a way to test the converter # C56217. Use a circuit tester such as # PTW2993 or your meter to test the yellow input wire (on the side that has more wires going into the box) while the left blinker is activated. If there is no power on that wire, then it is a problem on the vehicle side that will need to be tracked down.

If it does have power going into the box but not coming out, then that indicates a problem with the converter and the harness will need to be replaced. I recommend # 118449.

It is unlikely a ground problem based on all of the testing you have already done.

expert reply by: Michael H