Trailer Lights 101

trailer lights
Trailer lights are not only required by law, they are a necessary safety item. Photo provided by author

Almost everyone with a fishing boat has either gotten it wet already or will in the near future. But one of the most aggravating aspects of pulling a boat is the unreliability of trailer lights, especially when they are a necessary safety item.

I have never owned a boat trailer, or any trailer for that matter, that didn’t eventually have light problems. Ironically it was always at the most inopportune time, like when I’m ready to leave on a trip. Even though everything was checked the evening before, it seems like gremlins would somehow crawl into the wiring during the night. Sometimes problems were fixed in minutes and other times end up with the entire wiring system being ripped out then replaced. But since then I’ve learned a few things.

The best way to troubleshoot trailer lighting is to begin giving the rig a good, visual inspection. That involves checking the truck to trailer connection, which is usually the biggest problem with faulty lights.

The next most common problem is usually an improper ground. Symptoms like flickering or erratically working lights are a tell-tale sign. Trailer wiring is usually grounded one of two ways, either from direct contact between trailer hitch and ball or by a dedicated ground wire from the wiring harness which is attached directly to the trailer.

It is very important to make sure the ball and trailer coupling is free from rust. I usually put a small amount of light oil or penetrating oil on a rag and wipe them down. If you have a separate ground wire make sure the connection is good, which in some cases may entail scraping a bit of paint away. With all the grounds checked make sure all the wiring on the trailer is intact with no breaks, rubbed spots or nicks.

Next check all bulbs and fixtures. Look for broken filaments or discoloration. Look for water trapped inside the fixture. When in doubt replace connections or bulbs.

Water and electrical components are natural enemies so it’s no wonder trailer lights can be fickle. Trailers with submersible lights aren’t exempt from having issues either, even though they say you can leave them plugged in continuously. But if your trailer has the standard 1156 or 1157 incandescent lights make sure you always unplug them before backing into the water. Another good idea is to rub a light coating of electrical grease on the bulb bases to help keep water out and reduce rust and corrosion.

I personally favor the new LED lights. LED stands for “light emitting diode,” in case you wondered. A tiny diode gives off light when a small electric current passes through it. These lights are brighter and faster than regular bulbs. They also last longer because they can take road vibration and shock. They don’t have a delicate hair-like filament prone to breakage.

LED’s also illuminate faster. They light up instantaneously. In comparison, incandescent lights require one half a second to reach 90 percent illumination. They do make LED bulbs that can fit into traditional incandescent fixtures, however it is not recommended to mix the two. Regular bulbs draw much more amperage than LED’s and can cause the LED to burn up.

John Martino
Martino is a well-known outdoor writer throughout Indiana and has served as longtime outdoor columnist for the Kokomo Tribune newspaper. Martino has won numerous awards for both his writing and his service to youth, conservation and the community. He recently retired as Superintendent of Parks and Recreation for the City of Kokomo and now works as Ivy Tech Executive Director for Facilities for the Kokomo region.


  1. My dad has a boat wherein its trailer lighting has been grounded. Since we have basic troubleshooting steps knowledge on this aspect, we immediately ask for a professional help. Now, we let him check the boat from time to time or as schedule as its maintenance. And yes, I recommend it, really a must thing to do!


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