Troubleshooting Right Side Turn/Brake Signal on Boat Trailer

Question:

All of my boat trailer lights work when the truck lights are turned on. The left side turn signal and brake lights work. The right side turn signal and brake ligh do not work.

asked by: Chris

Expert Reply:

The first step would be to determine if the problem exists on the tow vehicle or on the trailer. Use a circuit tester like part # PTW2993 on the trailer connector at the rear bumper of the vehicle. Activate the right turn signal, and for a 4-pole trailer connector, test the pin that is fed by the green wire. For a 7-way trailer connector, test the pin in the 3:00 position. With the turn signal on, the tester should blink along with the turn signal. Pressing on the brake pedal should also light the tester. Now turn on the vehicle head lights and test the running light pin. On a 4-pole, it is the pin fed by the brown wire. On a 7-way connector, test the pin in the 11:00 position. Make sure the connector is not corroded or damaged.

If everything checks out here, you have successfully confirmed that the problem is in the trailer wiring. If the right turn, or running light pins do not light up when each function is activated, the probable cause is a blown fuse or a loose wire somewhere on the vehicle. Fuse locations can vary by vehicle. Most factory tow package circuits are protected by fuses located under the hood in a fuse box. If the fuses check out OK, examine the trailer connector for loose wires or connections.

Next, turn your attention to the trailer. Closely examine the trailer connector, looking for corrosion on the pins and sockets. Corrosion can prevent voltage from the tow vehicle from reaching the lamps on the trailer. Make sure the white ground wire is securely grounded to the trailer frame, and that this connection is not compromised by corrosion. Examine the wiring itself, especially the green wire that typically feeds the right turn and brake lamp. Look for a loose connection or or broken wires. Make sure the wire insulation is not cracked or worn. Check that the wire connections at the lamps are secure. Check the bulb and its socket for corrosion. The trailer running lights are usually fed by the brown wire. Typically, at some point on the trailer, the running light circuit will split into two legs, with one leg feeding each side of the trailer. Find the location where both sides split up, and make sure this connection has not come loose.

expert reply by: Chris O