How to Test and Fix Your Boat's Navigation Lights

At dusk or in a shaded spot, turn on the navigation light switch. Walk all the way around the boat (or have a helper on the dock). Confirm the red light is on the port side, green on starboard, and the white light(s) are lit and visible from all the angles they should be.

Many helms have a NAV position and an ANCHOR position, or two switches. Select anchor. Only the all-round white light should be on. If the sidelights stay lit in anchor mode, or the white light does not come on, note it for the switch check.

If a light is out, tap the lens and housing gently with your finger. If it flickers, the bulb's contacts or the socket are loose or corroded. That is usually a cleaning job, not a new fixture.

On boats with a stern pole light, pull the pole and look into the base on the deck or gunwale. These bases sit in spray and rain, and their contacts corrode. Clean the pins in the base and on the bottom of the pole until they are bright. Seat the pole fully and twist it until it locks. Light the pole up again.

Remove the lens screws or snap-off cover. Look for water inside, green or white corrosion, a blackened or loose bulb, or a cracked lens or torn gasket. Water inside the fixture is the root cause of most repeat failures.

Pull the bulb and look at the filament. If it is broken or the glass is black, replace it with the same type. If it looks fine, clean the bulb base and the socket contacts with fine sandpaper, an emery board or a pencil eraser. Put a light film of dielectric grease on the contacts and reinstall.

If the light still does not work, set your multimeter to DC volts. With the switch on, touch the red probe to the positive wire at the fixture and the black probe to the negative wire. You should see close to battery voltage.

• Voltage present, light dead: the bulb, LED or fixture is bad, or the socket has a bad contact.
• No voltage: the problem is upstream in the wiring, switch, fuse or breaker.
• Low voltage: look for a corroded connection somewhere along the circuit.

At the helm, check the fuse or breaker for the nav light circuit. Replace a blown fuse only with the same rating. If it blows again, there is a short: stop and find it before replacing more fuses. Test for voltage going into and coming out of the switch. Switches that crunch, stick or work only sometimes should be replaced.

Follow the wires from the helm to the light, especially where they pass through the anchor locker, under the gunwale, or through hatch hinges. Look for wire ties that broke, letting wires sag and get snagged, crushed or pulled apart. Check any connection that sits low or in the bilge.

Cut out damaged wire and splice in new tinned marine wire with heat-shrink butt connectors, then shrink them to seal. Keep splices high and dry. Do not use household twist-on connectors or tape-only splices.

Replace a cracked lens or a hardened gasket. If the housing is corroded inside or the lens is cloudy, replace the whole fixture. If you install LED fixtures, check the polarity: LEDs only work one way, so a reversed wire can look like a dead light. Buy by the label, not the picture. Under federal rules (33 CFR 183.810), a certified navigation light carries a permanent label you can read without taking it apart, with "USCG Approval 33 CFR 183.810," the testing lab, the model, its visibility in nautical miles and the bulb it was tested with. Lights too small for the label are marked "USCG" plus the range, such as "USCG 2nm." Cheap look-alike lights often skip all of it.

Check the arc too. A masthead light must cover 225 degrees forward and a stern light 135 degrees aft. The Coast Guard once warned about an LED light sold as a "masthead" or "navigation" light that only covered 180 degrees and met no requirement at all.

After any LED upgrade, do the radio check the USCG described in a safety alert: some LED lights quietly reduce VHF and AIS reception, especially masthead lights close to the antenna. With the LEDs off, tune the VHF to a quiet channel and turn the squelch up until the hiss just stops. Turn the LEDs on. If the radio starts hissing, the lights are raising the noise level and your radio may miss calls. Move the light or wiring, or replace the fixture with a better-filtered one.

Repeat the walk-around test in both NAV and ANCHOR modes. From out on the water or a distance away, make sure nothing aboard blocks the white light, such as a T-top, Bimini top or outboard cowling. Log the repair in BoatMend.