How to Troubleshoot Utility Trailer Light Wiring
- 1). Disconnect the trailer from the towing vehicle. Park on a level surface, engage the brake and chock the tires.
- 2). Remove each light from the trailer by removing the nuts holding them in place and disconnecting their wires. The two marker lights and the license plate light each have a brown power and a white ground wire; the left taillight has a brown power, yellow brake/turn and a white ground wire; the right taillight has a brown power, green brake/turn and a white ground wire.
- 3). Inspect each ground point where the white wires attach to the trailer frame. They must be unpainted and free of corrosion.
- 4). Check for continuity between each ground wire and its corresponding light with an ohmmeter. Each should show a closed circuit with little resistance, meaning there should be an ohm value, but it should be minuscule.
- 5). Inspect for continuity between the exposed yellow wire at the left taillight and its pin on the electrical connector. Also check the brown wire's continuity from the left taillight to the left marker light, then the marker light to the connector. Again, each should show a closed circuit with little resistance.
- 6). Inspect for wire to wire shortages by attaching one meter lead to the exposed taillight brown wire and the other lead to the yellow wire. The meter should read an open circuit. Repeat for the marker light brown wire to the yellow wire.
- 7). Check for shortages to the ground, which is the trailer frame, by attaching one meter lead to the marker light brown wire and the other lead to a clean, bare metal ground point. Also check the brown and yellow wires at the left taillight to the ground independently. Each should show an open circuit.
- 8). Perform the continuity and short inspections for the right side wiring, substituting the yellow wire in the steps with the green wire.