Troubleshooting Boat Trailer Light Problems

Laws vary from state to state, but essentially you’re required to have working tail lights, brake lights and turn signals on your boat trailer as you would on your car or truck. 

Boat trailer lights troubleshooting

Boat trailer lights are notorious for failing due to a variety of electrical problems, so it would save you some time and maybe a few headaches to know how to fix them yourself. Unless of course, you like getting traffic citations. Here are some troubleshooting tips for dealing with boat trailer light problems. 

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Problem: Single Light Not Working

A blown bulb is likely the cause of a single boat trailer light not working.

Boat trailer light

Troubleshoot: Remove the bulb, then clean the electrical connector behind the bulb with fine grit sandpaper or wet/dry paper, and install a new bulb. Otherwise, if the existing light uses fragile incandescent bulbs, consider replacing the complete light unit with a new one using long-life LED lights.

Problem: Whole Light Function Not Working

A blown fuse is the likely culprit for a boat trailer’s tail, brake or turn light not working.

Lights on a boat trailer

Troubleshoot: If the light system uses an inline fuse, check the fuse and replace it if it’s burnt out. 

A damaged or broken wire could also be to blame for a whole boat trailer light not working. 

Troubleshoot: Run a continuity test by connecting one end of a continuity tester to the end of a wire at a light, and the other end of the continuity tester to the other end of the same wire at the trailer-to-vehicle connector. If the tester lights up, the wire is good. Move on to each wire until the bad wire is identified, and replace that wire.

Problem: All Lights Not Working

When not a single light on your boat trailer is working, the vehicle-to-trailer 4-way plug is usually the suspect.

Boat trailer lights electrical problems

Troubleshoot: Disconnect the vehicle to trailer 4-way connecter, then use electrical contact cleaner spray to clean any dirt or debris from the 4-way flat plug. Test the electrical power coming from the tow vehicle with a 4-way tester. If the tester indicates a problem, the blame lies with the electrical current coming from the towing vehicle and not with the boat trailer lights.

Boat trailer electrical problems troubleshooting

Another reason none of your boat trailer lights are working could be a bad ground connection.

Troubleshoot: Remove the ground wire (or each individual ground wire) from the trailer frame, then make sure the wire’s connector and the frame can make good metal-to-metal contact by cleaning the contact points with fine grit sandpaper or wet/dry paper. If the ground wire’s screw or bolt is corroded, replace it with a new one. Reinstall the ground wire to the trailer frame and ensure the connection is tight.

Problem: Lights Working Intermittently 

When your boat’s trailer lights only work intermittently, the likely culprit is worn or damaged wiring.

Fixing boat trailer lights

Troubleshoot: Replace the trailer’s complete wiring system, which is much easier than hunting for and testing individual problematic wires. Trailer light kits include all the necessary wiring, and also present the opportunity to upgrade from unreliable incandescent lights to durable LED lights.

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