Trailer Wiring Harness on 2009 Toyota Matrix is Not Working, No Trailer Lights  

Question:

Expert Reply:

The first thing to check on trailer wiring harness # C56035 for your 2009 Toyota Matrix is the fuse for the power wire that connects to the vehicle battery. This harness gets power for the trailer lights from the vehicle battery so if the power wire is not connected to the battery or the fuse is missing or blown then the trailer lights will not work.

Also make sure the white ground wire is attached to a clean, bare metal surface; preferably by itself. There can be no paint or coating at the ground location.

To test to see if the harness' black converter box is the problem use a circuit tester such as # PTW2992 or a meter if you have one to test it. Have someone sit in the vehicle to operate the lights. Then test the wires going into the converter box from the vehicle. If the input wires show power when they are supposed to then you can move on to the next part of the test. If they do not show power when they should then there is a problem on the vehicle side. Check the connectors on the harness and vehicle for any broken or bent pins and repair as needed.

If the input side is good then move on to checking the output wires (4-Way end) in the same way. If the output wires do not show power when they should but everything is fine on the input side then that indicates a problem inside the converter and the whole harness will need to be replaced.

If everything is working on the input and the output side then the issue is on the trailer; likely a bad ground. This sounds like a ground issue. Ground problems normally show up when there is more draw on a system such as when you have the running lights on and then use another function like a turn signal or brake light but can show up any time.

Make sure that the vehicle side and trailer side connectors are clean and free of corrosion inside and out. The main connector grounds should be attached to clean and corrosion free bare metal surfaces.

The light grounds should also be attached to clean and corrosion free bare metal surfaces. If there is anything between a light ground and the metal trailer frame or if the trailer has an aluminum frame, tilt bed, or folding tongue, any of these things can interrupt the ground. Running jumper wires from the light grounds to the main trailer connector ground can help.

expert reply by: Michael H

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