How to Replace Boat Trailer Lights

How to Replace Boat Trailer Lights


When one considers the time and effort involved in maintaining a boat, rarely does the trailer get mentioned.

The items that come to mind are things such as keeping the hull in good condition, making sure it gets cleaned, regular motor maintenance, keeping your sails in good shape if you own a sailboat, winterizing, moorage, and more. Normally, the trailer the boat sits on and what it takes to ensure it stays serviceable takes a back seat to the boat itself—but should not be overlooked. After all, what good is a boat if you can’t tow it to the boat ramp?

Recently, a hand-built wooden sail boat came in to my posession that I’ve been storing, for the most part, without seeing much use. Part of the reason is that the trailer lights were never operable and I kept putting off replacing them for a couple reasons.

The trailer is from the 1960s and the requirements for legal tail lights has changed over the years (side reflectors, size, etc.). Back in 1960 all I would have needed are a couple of small round lights, but now there are size requirements, thus rendering the mounting point too tight for modern lights.

The old light was mounted improperly due to the space constraints between the bolt on the left and the frame on the right.

And, I still have to learn to sail, so it was hard to argue that it was worth my time and effort to replace the tail lights in the first place.

I had a couple of grand notions, such as finding custom lights or even 3D-printing the housing that would actually fit the awkward corner of the trailer where they had to go. I decided to buy the modern lights and get creative. However, the process for actually installing trailer lights is pretty universal from trailer to trailer.

I ended up buying a decently cheap pair of LED marine tail lights, but it’s worth noting that they didn’t come with all the necessary hardware, and the instructions were flat-out wrong at one point (we’ll discuss in a moment).

The full contents of my lighting kit: two side-markers, two taillights, license plate mount, and wires. Electrical tape, wire connectors, and mounting tape purchased separately.

It came with the lights and the wires, but no other items required for installation. Ultimately, this is how I expected them to arrive, but the instructions that were included allude to other items such as electrical connectors and mounting hardware that were not in the package from the manufacturer. Keep in mind that you’ll need items such as quick-splice connectors, electrical tape, weatherproof mounting tape, and maybe some zip ties. Here’s a run-down of my hardware list:

  • quick-splice connectors
  • wire strippers/crimpers
  • Leatherman Wave multi-tool
  • Plastic zip-ties
  • Multi-meter

The first order of business was to remove the old non-marine lights that were installed backward and broken by the previous owner of the boat. Just unbolt the lights and remove them with the wiring.

With the old lights removed you can begin assessing your project. Things to keep in mind are how they mount to the trailer (likely a standard mount with two bolts), how long to make the wires, what kind of connector do you need for your vehicle?

The lights came with plenty of length in the wire that routed to a flat-four trailer wire connector to accommodate most boat trailer lengths. With the lights more or less in their final position (you don’t need to secure them at this point) you can trace the length of the trailer with the wires until you meet the hitch and then leave enough to make it to the connector under your vehicle’s bumper. If you make the measurement exact then you may be stretching/breaking your wires as you tow your boat; be sure to leave a little extra to account for the articulation.

You have two options at this point:

  1. Cut the wires at-length and splice in the appropriate connector
  2. Bundle the excess wire and tuck it in to the trailer frame

I opted to cut the extra wire and splice the connector back in because I was going for the cleanest possible wiring job.

The next hurdle to overcome was where and how to mount the side-marker lights. I was lucky enough to have small holes in the frame about half-way down the length of the trailer that fit the wiring ever-so-snugly. Even though the side-markers had screw-mounting holes I opted against trying to drill mounting holes in the frame and used all-weather mounting tape, instead.

I found all-weather mounting tape to be sufficient to secure the lights to the trailer frame.

There was some confusion, though, on how to wire the lights. The instructions explicitly stated that both of the wires coming out of the back of the light were to splice in to the positive wire. It didn’t make any sense to me but I followed the instructions and made sure not to affix the lights with tape before testing them. That was definitely a good idea.

Be sure that one wire goes to the power and one wire goes to the ground, otherwise the side-marker lights will not operate.

With the lights now operable I could tighten everything down and mount everything in final positions before routing the wires. I found it easy to tuck the wire behind the frame structure and then wrap a zip-tie around the frame to keep them in place.

With the taillights and side-markers mounted, wires run and secured, and the connector spliced in you’re finished, provided you hook the trailer up to your vehicle and they all function appropriately. A proper lighting job will last a long time as long as you use the correct equipment and materials and, chances are, you may never have to touch them again.


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