How to Hook Up and Install Trailer Lights: A Step By Step Guide

Though your boat is built for the water, there will be plenty of times when you will have to lug it around on land. As you take your boat from point A to be point B, the road requires you to have trailer lights so that other drivers can see that you are transporting a boat, as well as what moves you’re going to make while driving. If other motorists don’t know you are carrying a trailer due to there being no trailer lights on your boat, you could cause a serious accident and injure yourself and others. To avoid a serious or even fatal collision, you can easily install trailer lights without problem. The following step by step guide will walk you through how to hook up and install trailer lights.

Starting with the Basics

Installing electrical fixtures on your boat or trailer is a pretty straightforward process, but it can be dangerous if you do not know what you’re doing. Before you do anything, you need to know how to hook up an electrical outlet on your boat. This will be useful not only for trailer lights, but also for cell phones chargers, kitchen devices like hot plates, using a laptop or tablet, an even plugging in lamps and other light fixtures. Once you have a handle on hooking up an electrical outlet, you can move on to hooking up and installing trailer lights.

In addition to electrical wiring basics, you should pay attention to trailering basics. Trailering is as much a part of boating as getting out on the water. The products (such as tail lights and tires), procedures, and precautions involved with trailering are all part of ensuring that you when you go boating, you’re safe on land and on sea.

Hooking Up and Installing Trailer Lights: What You’ll Need

Each of these items can be found at your local hardware store or your local boating store. Some parts may vary depending on the size of your boat and trailer. The 4 wire trailer light connector and harness are one of the most common set ups for small and medium boat trailers as well as small utility trailers.

Once you have your tools and materials, be sure you have an hour at most to work. The whole process should take less than that, but you want to have some wiggle room for mistakes or setbacks.  

Hooking Up and Installing Trailer Lights: The Process

Step 1: Locate a the tail light wiring harness. This can usually be found inside the trunk of the trailer near the back bumper. Once you have found it, begin looking for an area for the harness clamp for the four wire trailer light connector and harness. This connection is usually made beneath the back bumper so be sure to scout that area mainly.

Step 2: Take your drill and create a ⅛ inch hole in the car frame near your connector location.

Step 3: Attach the wiring harness clamp to the light connector using a sheet metal screw through the ⅛ inch hole.

Step 4: Once done, be sure to leave six inches of the end wiring harness with the connector hanging from the wiring harness clamp. Then, drill a ½ inch hole into the bottom of your trunk near the location you previously scouted out beneath the bumper where the four trailer light wiring harness will be connected to the tail light wiring harness.

Step 5: Guide the other end of the wiring harness (note: not the connector end) through the ½ inch hole you made in the trunk.

Step 6: Locate the green wire in the tail light wiring harness. This will power the right side, stop, and turn light. Use a wire splice and attach the green wire from the four wire trailer connector harness to the green tail light wire. It’s simple enough: match color to color!


Step 7: Next, locate the yellow wire in the tail light wiring harness. This will control the left side, stop, and turn light. Again, use the wire splice to attach the yellow wire from the four wire trailer light connector to the yellow tail light wire: again, match color to color.

Step 8: Finally, take the brown wire in the tail light wiring harness. This wire will power the tail, license, and marker lights. Take the wire splice and use it to attach the brown wire from the four wire trailer light connector to - you guessed it - the brown tail light wire.

Step 9: Using your drill, create an ⅛ inch hole in an open area of the metal frame inside the trunk.

Step 10: Once the hole has been drilled, take your sandpaper and use it to smooth out the metal a half inch (1/2  inch) of the ⅛ inch hole. Be sure to keep sanding until all paint, varnish, shine, and other materials are totally gone. You just want a smooth space of metal.

Step 11: Once the metal has been smoothed and cleaned, attach the white wire from the four wire trailer light harness to the ⅛ inch hole using a sheet metal screw.

Step 12: Once all the wires are connected, test the wiring by turning on the headlights. Be sure to clip the ground side of the test wire to the ground wire connection screw.

Step 13: Place the pointed end of the test light into the green wire of the four wire trailer light harness. If the test light turns on when this is done, you know the connection is good and all has been done correctly! Once you have confirmed this, turn off the headlights.

Step 14: Turn on the right and left side turn signals respectively. See if the test light blinks. If so, the connection is good. Remember the green wire is for the right side, while the yellow wire is for the left.

Step 15: Have a friend step on the brakes to see if the test light comes on. If so, the connection is good!

Step 16: Finally, close up the ½ inch hole you created in the trunk using silicone or another water tight sealant. This will ensure that water and other unwanted substances stay out of the trailer in wet, dry, or harsh conditions. Next, cover up the white wire to the frame using silicone or another sealant to avoid rusting erosion.

And you’re done! Remember, electrical wiring can be tricky, so it is important to take precautions when working with electricity on boats and boat trailers. If sparks are to fly or a fire breaks out, you’ll want to have the right kind of fire extinguisher nearby.

Once you have your trailer lights properly installed and hooked up, you can hit the road. This means that if the mood strikes you to try fishing on another lake in another state, nothing is stopping you from hopping in your truck and heading out! Being out on the water is always a great time, and proper boat safety makes things even better. We hope this guide was useful and that you will have an easier time enjoying your next trek out to the water!