How to Wire Boat Trailer Lights

by Will Charpentier

Sooner or later, you'll need to get the lights on your boat trailer in working order if for no other reason than "staying legal" and staying safe while towing your boat. Fortunately, the quick connect wire connectors used to hook up most boat trailer light wiring is fairly standardized: there's a brown wire for the tail lights, a green wire for the right turn signal and a yellow wire runs the left signal. The connections are made to the tail light wiring harness at the lights or under the bumper, and the quick connect provides the junction between this point and the trailer's wiring.

1. Look under your bumper and see if the tail light wiring is visible; if not, then remove one tail light lens, the red plastic cover over the bulbs for the tail light, the brake light/turn signal and the back-up light and set them aside to be re-installed later. Instructions for removing your tail light cover are in your car's owner's manual, but often, the tail light cover is removed by using a screwdriver to remove the screw(s) around the edge of the tail light lens.

2. Pick a place to attach the quick connect harness clamp to your car, preferably on one of the bumper mounts. Before drilling the mounting hole, make sure that the harness, if mounted at that point, will be able to reach the trailer connector. If so, use a drill to make a 1/8-inch hole at that location and use a self-tapping metal screw to screw the clamp in place. Attach the white ground wire of the quick connect harness to this screw as well by wrapping it clockwise around the screw before tightening the screw with a screwdriver.

3. Clip the test light's alligator clip to a clean spot on the vehicle's chassis to act as a ground for the light and turn on your head lights. This also turns on your tail lights, one of which has its bulbs exposed. Use the probe end of the test light to touch the exposed wires in the uncovered tail light until you touch the one that makes the test light come on steadily. Connect this wire to the brown wire of the quick connector.

4. Turn your ignition switch to the "On" position and activate your right turn signal. Again, use the probe on the test light to find the tail light wire that lights the bulb of the test light. Connect this wire to the green wire on the quick connector. Turn off the right turn signal and turn on the left, and repeat the probing process. Connect the wire that lights the test light to the yellow wire of the quick connector.

5. Start your car and have an assistant watch your car's tail lights and the trailer's lights. Turn on your headlights, check the operation of the left and right turn signals and, since the same bulbs used for the turn signals serve as the brake lights, step on the brake. If everything is in good order, re-attach the tail light lens you removed to make the wiring connections.

Items you will need

  • Automobile owner's manual
  • Screwdriver
  • Quick connect wiring harness
  • Drill
  • Self-tapping metal screw
  • Test light with probe and alligator clip
  • Assistant

Tip

  • The type of test light most suitable will have an alligator clip mounted on a wire running from the light pen. The light pen will have a probe at its point, and the probe will be surrounded by the lens for the "Power Indicator" light. This will let you maintain the same ground contact even when you move the test light around.

Warnings

  • This project involves electrical work; appropriate caution is recommended.
  • Whenever you connect or disconnect your trailer, and before you begin each tow, check the lights to ensure that they're in good working order.

About the Author

Will Charpentier is a writer who specializes in boating and maritime subjects. A retired ship captain, Charpentier holds a doctorate in applied ocean science and engineering. He is also a certified marine technician and the author of a popular text on writing local history.

Photo Credits

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