Navigation lights are safety equipment, and they fail in a small number of very predictable ways. Bulbs get blamed most often and are rarely the culprit. Salt laden air, vibration and long cable runs up a mast do far more damage than filaments do.
Because a light that works at the dock and fails at sea is worse than one that never works, chasing intermittent faults properly matters.
The usual suspects are the mast base plug, the deck gland, the fixture terminals themselves and the negative return. Green powder, a chalky white bloom or a wire that crumbles when flexed all point the same way.
An intermittent that comes and goes with heel, engine vibration or halyard slap is almost always a mechanical connection problem rather than a component failure.
A masthead light at the end of a thin, long cable can see noticeably less voltage than the panel does. Filament lamps go dim and yellow, and some LED units flicker or fail to strike at all.
Measuring at the fixture with the lamp connected and drawing current, not at the panel, is the only way to see this.
Swapping a filament lamp for an LED changes the load dramatically. Old failure detection circuits may report a fault, dimming circuits may misbehave, and cheap units can generate radio interference that ruins VHF reception and AIS.
Fixtures also carry approvals as a complete unit, so dropping an LED bulb into a housing designed for a filament lamp is not always a like for like change. If the light is doing a legal signalling job, fit a unit intended for the purpose.
Checking a fuse, cleaning an accessible connector and confirming the switch works are all reasonable owner jobs at the dock. Climbing a mast, or working on wiring you cannot see the whole run of, is not, and neither is sailing at night with a light you are not sure of.
Almost always voltage loss or a poor connection somewhere in the mast wiring, most often at the base plug or deck gland where water gets in.
Yes for power consumption and lamp life, provided you fit approved fixtures rather than swapping bulbs into old housings, and check for radio interference afterwards.
It can. A chafed cable or a shared negative fault often shows up first as a flickering light and later as something more serious, which is why it is worth tracing properly.
We trace mast and deck wiring, fix the connections properly and test under load, so the light works when it matters.