Lights on Trailer are not Working and Fuse is Blown on Curt T-Connector # C5621

Question:

I have a 2015 Toyota Highlander and a 4 x 8 trailer. The lights and blinkers always worked, however, today they didnt. The first thing I did was rewire the entire trailer. I figured there must be a short somewhere. However, after rewiring, I still didnt have any lights or blinkers. Then I found that the fuse had blown. I had placed a 10amp fuse which was provided by the 3rd party manufacturer of the harness Curt, I believe when Toyota recommends a 30a fuse. So, placed a 30a fuse in the panel. Still nothing. Finally, I then checked everything all over again and again and again. I though that maybe I wired the rear lights and blinkers wrong, so I changed that around several different ways. I also checked that the white wire was solidly connected to the ground screw at the frond of the trailer. Im at a loss. Could the blown fuse have destroyed all of the lights and blinkers? Could the part of the harness that is wired directly to the car have a problem? Please help.

asked by: John

Expert Reply:

I believe that the Curt T-Connector that is installed on your 2015 Toyota Highlander is part # C56217. Since it comes with a 10amp fuse you will want to make sure that you continue to use a 10amp fuse because the fuse relates directly to this wiring harness and connector - not what Toyota has. Using a larger fuse can result in damaged wires and could possibly start a fire since a fuse is meant to prevent a system from overloading.

From the troubleshooting that you have already done it sounds like the problem is on your Highlander. You can verify this by testing your Highlander and trailer separately. Use a Circuit Tester #PTW2993 to see if you are getting power to the connector on your Highlander and use a 12V power source, like the battery from your Highlander, to test the connector on your trailer. If your Highlander connector sends the correct signals, then the problem is your trailer. If your trailer lighting works, then the problem is on your Highlander.

Since your 10amp fuse was blown what you are looking for is a short. This can be the result of corrosion inside the connector on your Highlander of trailer or any of the grounds on your trailer of Highlander not being connected to a clean, bare metal surface. This includes any ground that is connected to an individual light. You will also want to check the wiring on both your trailer (which it sounds like that should be in perfect shape) and your Highlander and look for any places where the wiring might be bent, exposed, corroded, or damaged. You will want to clean any corrosion and replace any damaged wires.

If you search both the Highlander and your trailer for these symptoms and still cannot find the issues, then you will want to take your setup to a qualified mechanic who can physically inspect it for you as well. Sometimes it helps to get a fresh set of eyes to look over something.

expert reply by: Jon G