“Probably Just The Bulb”
One of the most common statements I hear during pre-offer conversations is, “I’m sure it’s just a bulb.” A light is out on the masthead, the steaming light doesn’t come on, the spreader lights are dark—and the seller assumes a quick, inexpensive fix. But on a 25–30-year-old sailboat, a non-functioning light aloft is often the first clue of a much deeper issue.
In one recent case, the buyer was told exactly this. After the sale, their rigger went up the mast to “pop in a new bulb” only to discover that the wiring inside the mast was so aged that the copper conductors literally crumbled on contact. The failure wasn’t the bulb—it was the entire wiring run, from masthead to exit, which now required a full replacement. A fix that costs a few dollars quickly became a major job.
This kind of scenario isn’t rare—and it’s precisely why electrical non-function aloft should never be brushed off.
Why Mast Wiring Fails Over Time
Electrical wiring inside a mast lives in one of the harshest micro-environments on a boat. Even on well-maintained vessels, several factors contribute to deterioration.
1. Tinned vs. Untinned Copper
Older boats (especially early 1990s or before) often used untinned copper wiring.
Untinned copper corrodes much faster in a marine environment.
Over decades, oxidation travels under the insulation, weakening the conductor.
When the insulation is stripped back, the wire appears black, brittle, or powdery—and can literally break apart when handled.
Modern ABYC standards recommend tinned-copper, marine-grade wiring because the thin layer of tin dramatically slows corrosion and improves longevity.
2. Moisture Intrusion Inside the Mast
Even though a mast looks sealed, it’s not. Water gets in through:
sheave openings
masthead fixtures
deck partners
condensation
This moisture tends to migrate along wiring and sits in low spots, slowly wicking into the insulation. Over the years, that environment corrodes the copper and stiffens the insulation, especially where the wire is cable-tied to the mast interior.
3. UV Exposure at Entry/Exit Points
At the masthead and spreaders, wiring is exposed to UV through small openings. UV degrades insulation, causing it to:
crack
split
lose flexibility
UV-damaged insulation exposes copper to air and moisture—accelerating decay.
4. Mechanical Fatigue and Vibration
Sailboats experience constant mast vibration underway and at anchor. Over decades:
wire strands work-harden
connectors loosen
chafe develops where wires run through small apertures or against halyards
movement at masthead fixtures stresses spade or bullet connectors
On older rigs, this movement alone can break already weakened conductors.
5. Heat Cycles and Old-Era Manufacturing
Thirty-year-old insulation materials are not what they are today. Many older wiring harnesses used PVC that becomes rigid over time, trapping moisture and cracking when flexed.
Buyer Takeaway
When a seller casually says, “It’s probably just a bulb,” treat that statement as a starting point for investigation, not an answer. A dark masthead light—especially on a decades-old sailboat—is often a red flag for compromised wiring aloft. Replacing mast wiring requires lowering or climbing the mast, pulling a new chase, replacing connectors, and inspecting fixtures. It’s a job measured in hours (and sometimes thousands of dollars), not minutes.
Small comments can hide big expenses—and this is exactly what the Buyer Watchouts section is all about.