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Solved problems · Electrical · Crew answer

Why aren't my navigation lights working?

When a nav light fails and the bulb is fine, the cause is usually a corroded or strained connection, often at the mast base or bow. Here's how to trace it with a meter.

Symptom

A running light, steaming light or masthead tricolor is out, dim or flickers, often after rain or a rough passage, or works only when the switch is wiggled.

Likely cause

Nav light circuits live in wet, exposed places. Corroded sockets and terminals, a water-filled deck plug at the mast base, a broken wire inside the mast, a failed switch or breaker, or undersized wire on a long mast run all cause outages or dimming. LED fixtures can fail internally or misbehave at low voltage.

Stop now if

You see heat damage, melted insulation or a breaker that trips right away. Leave it off and find the short. Never go aloft without a proper bosun's chair or climbing harness, a second halyard as a backup, and an experienced person on the winch. Without working lights, don't run at night. The navigation rules require them from sunset to sunrise and in restricted visibility.

The fix, in short

  1. Check the obvious first. Confirm the breaker or fuse and switch are on, and swap the bulb or test the LED fixture if it's easy to reach.

  2. Measure voltage at the fixture. With the light switched on, measure volts across the fixture's wires. Full battery voltage with no light means the bulb, LED or socket. Zero means the fault is upstream.

  3. Test the mast-base or deck connector. Many mast-light failures sit in the deck plug or junction near the mast base. Measure voltage on both sides of it and look for green corrosion or water inside.

  4. Look for voltage drop. With the light on, compare battery voltage to the voltage at the fixture. ABYC guidance cited by Cruising World allows only about 3 percent drop on navigation light circuits. More points to corroded joints or wire that is too thin for the run.

  5. Repair with marine-grade parts. Make connections with marine heat-shrink terminals and tinned wire, support the wire so its weight doesn't hang on the fixture, and protect it from chafe where it passes metal edges.

Written by Sailor Cruiser crew. General guidance, not an inspection of your boat.

Equipment involved

  • Navigation lights: Sidelights, sternlight, steaming light, masthead tricolor, deck plug and mast wiring

Related guides

Sources

Background reading we checked while writing this answer. The wording above is our own.

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