How to Repair Boat Trailer Lights

Test and repair your boat trailer lights.

It is necessary to have all your trailer lights properly working when towing your boat. Most boat trailers use only four wires for the lights. Many different adapters can be purchased from trailer and auto parts suppliers to match almost any configuration differences from the vehicle to the trailer. Check your lights each time you connect your boat trailer to safely tow your boat.

Things You'll Need

• Phillips screwdriver
• Flat screwdriver
• 12-volt probe tester
• Replacement bulbs
• Small wire brush

Instructions

1. Attach the trailer to your vehicle and plug in the wiring harness.

2. Determine the specific problem you have by having a helper get inside the vehicle and press on the brakes, turn on the clearance/side marker lights and activate the left and right turn signal lights while you observe. Make a note of any issues.

3. Check the ground or white wire for proper connection at the plug harness if none of the bulbs are illuminating. Make sure the wire is connected to a bolt on the frame. Remove any rust at the connection point with a small wire brush..

4. Remove the light covers of any dead side marker lights if some are illuminated and some are not. These are most likely bad bulbs and not a wiring issue. Check the filaments and replace with new bulbs if they appear broken or burnt.

5. Remove the rear tail light cover screws with a Phillips screwdriver, remove the cover and check the bulbs. These bulbs have two filaments. One is used for the clearance lights and the other is used for the brake and turn signal lights. Replace the bulbs if either of the filaments is broken. Many new boat trailers are now equipped with rubber gasket mounted sealed taillights. Unplug the wiring harness on the old light, plug in a new sealed unit and test. Replace as necessary.

6. Remove the trailer plug and check the wiring on both the vehicle and trailer. Look for any disconnected or frayed wires. Remove any corrosion from the terminals with a small wire brush. The brown wire carries the signal for the clearance lights, green is used for the right turn signal and right brake lamp, yellow carries the left turn signal and left brake light and the white is for ground.

7. Press the sharp tip of an electrical testing tool through the sheathing into each wire just behind the plug on the trailer side. Go through the testing steps in Step 2 to determine that the signal is passing properly from the vehicle to the trailer on the correct wire referred to in Step 5. The indicator light inside the tool will illuminate when power is transmitting through the wire. Retest the wire at the fixture to determine whether the wire is good or defective.

References

• Duckworks: Troubleshooting Trailer Lights