Trailer Running Lights Not Functioning After T-One Harness # 118558 Installed on 2012 Honda Pilot

Expert Reply:

As a first step, you should determine if the problem exists on the vehicle or on the trailer. Use a circuit tester like part # 40376 and test each pin on the trailer connector as its function is activated. Refer to the photo I edited to see which pin on the connector serves which function.

If you get a signal on the pin fed by the brown wire when the vehicle headlights are on, the problem is in the trailer wiring, and not the vehicle. Check the 4-pole connector on the trailer, making sure that it is not corroded or damaged. Make sure that the white ground wire leading from the connector is securely connected to the trailer frame. Trace the running light circuit (which is typically a brown wire) back from the connector to the lamps, making sure there are no broken or loose wires.

If you do NOT get a signal on the pin fed by the brown wire on the connector on the vehicle, check the relays and fuses that were installed along with the T-One harness. Make sure they were installed in the correct locations shown in the owners manual. The lid of the fuse box under the hood should have a legend showing which relays are installed in which location.

expert reply by: Mike L