Boat Trailer Light Troubleshooting

The lights on boat trailers are notorious for failing. Not surprising, considering the punishment they take on the ride to and from and in the water at the boat ramp.

Boat trailer light troubleshooting

When your boat trailer lights start acting up or stop working, here are some things you can do to troubleshoot the problem. 

NOTE: Before you try to troubleshoot trailer light problems, always disconnect the trailer tongue and any chains from the tow vehicle to ensure there are no electrical or ground circuits to the trailer that might give false readings.

Check Trailer Ground Wires

A bad ground connection is often the cause of trailer light issues. Tail lights flashing when a turn signal is used; lights flickering on and off; or lights simply not working can all be caused by a bad ground connection.

Troubleshooting boat trailer lights wiring

What to Do

  • Make sure all ground connections on the trailer frame are fully tightened.
  • Replace corroded ground connection screws or bolts. 
  • Repair any ground wires with bare wiring at their terminals by installing a new crimp terminal and heat shrink tubing.
  • Check for corroded ground connections. If you find any, detach them, clean the wire terminal and the trailer frame, then reconnect them. Cover the connection with dielectric grease to prevent further corrosion.

Check Fuses

If your trailer light system has an in-line fuse, check to see whether it has blown. And if fuses repeatedly blow, the circuit is probably getting overloaded and the root problem is elsewhere.

Boat trailer light problems what to check

Check the Vehicle to Trailer Connector

It’s possible the problem is with the vehicle-to-trailer connector or even with the tow vehicle itself and has nothing to do with the trailer’s light system.

What to Do

  • Clean any dirt or debris from the tow vehicle’s female 4-way flat plug by spraying it with electrical contact cleaner, and clean the trailer’s male 4-way flat plug too. Reconnect them and check if the lights work properly.
  • Test the tow vehicle by connecting a 4-way tester into the tow vehicle’s flat plug. The tester indicates whether the problem is with the electrical current coming from the tow vehicle.

Sierra trailer light LED tester

Sierra trailer light LED male/female tester

Replace Bulbs

When a single light isn’t working, it’s usually a blown bulb, especially if it’s an old-school incandescent light bulb. Remove the failed bulb, then clean the electrical connector behind the bulb with fine grit sandpaper or wet/dry paper and install a new bulb.


Anderson marine boat trailer light

Anderson boat trailer light kit

Check the Trailer Wiring

The wiring used on many trailers is notorious for causing problems with the lights. Badly corroded wires; wires that have worn through their insulation and are shorting against the trailer frame; and badly insulated connectors are all common faults with trailer lighting systems.

What to Do

  • Check wire connectors to make sure they’re tightly secure and free of corrosion, and replace any loose or badly corroded connectors.
  • Run a continuity test to isolate a faulty or broken wire. Testing a single wire at a time, attach one end of a continuity tester to the end of the wire at the light, and the other end of the tester to the end of the wire at the trailer-to-vehicle connector. If the light on the continuity tester fails to illuminate, replace the wire.

Troubleshooting boat trailer light issues

Replace Lights

Boat trailer lights are inexpensive, and simple to install. It’s often easier and more cost-effective in the long run to install new lights than to repair old trailer lights and electrical systems.

What to Do

  • Replace old incandescent trailer lights with more durable LED lights.
  • Install a new trailer light kit to avoid having to find and repair faults with worn existing wiring. Light kits come complete with brand new wiring sets.

Boat trailer lights how to troubleshoot




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