Troubleshooting Trailer Brake and Turn Signal Lights on Car Trailer Towed by Jeep  

Question:

Expert Reply:

Thank you for providing the photo of your Jeep trailer wiring. We can suggest troubleshooting steps to isolate the problem to either your Jeep wiring, connectors or trailer wiring.

First, securely attach the short white ground wire with ring terminal from the 7-way adapter to a clean bare metal surface on the Jeep frame. (Your photo shows this wire is not connected. This could be the problem.) You need to firmly attach all grounds to rust-free unpainted metal surfaces to ensure a good connection. Next check that there are no blown fuses in the Jeep fuse box.

If making the ground connection and checking fuses does not correct the problem, next we need to establish whether the 4-way connector on your Jeep is passing the correct brake and turn light signals from the lighting system. You will want to use a circuit tester such as # PTW2979 to test each wire. Apply the right turn signal on the Jeep and test for an on-and-off signal on the pin for the green wire. Repeat this step for the left turn signal on the pin for the yellow wire. If you do not detect on-and-off turn signals on the 4-way then the issue is within the Jeep wiring. You might want to refer to the wiring help article attached; if you scroll down past the photos you will find troubleshooting guidance.

If the 4-way has the correct signals then connect it to the 7-way adapter and re-test the pins on the 7-way. You can refer to the attached photo that shows which pin to test for each function. If the 7-way also has the correct signal then there is a problem with the trailer wiring and you can check for dirty or corroded connectors; loose, worn or pinched wiring; and loose ground connections, within the trailer. Connectors that appear okay may have slight corrosion (which can appear as a white or greenish film) on the connector pins. You can try cleaning these with a spray-on contact cleaner available from an auto parts or electronics store.

You do not indicate if your Jeep has ever before towed this trailer successfully. If not, it could be that the trailer lights simply draw too much current for the Jeep to handle. If the trailer has lots of marker lights, for example, you may need a powered taillight converter such as the Tekonsha # 119250KIT. (Note that this kit includes a circuit tester). Powered converters like this draw the power for the trailer lights from the tow vehicle battery, not through the tow vehicle taillight wiring.

expert reply by: Adam R

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