Underwater LED Lights: Care, Leaks, Corrosion, Wiring and the Rules

Note the brand, model, type (through-hull or surface-mount), housing material and where each light is. Find the controller, the fuse or breaker, and the cable routes inside the boat. Save the manuals in BoatMend; you'll need them for cleaning and repair rules.

With the boat in the water, open the access to each light from inside. With a flashlight and mirror look at:

• The housing nut and the sealant around it: any water, damp, salt crust or green or white corrosion
• The cable where it leaves the housing: water wicking along it, or a cracked cable gland
• The hull laminate around the housing: cracks, soft spots or a wet core

Why the core matters: in its installation how-to, BoatUS explains that in a cored hull the cut has to be dug out around the hole and filled with thickened epoxy, and even in solid fiberglass the cut edge should be sealed with epoxy, so a weeping seal can't let water into the laminate. If you don't know whether a previous owner did this, a surveyor's moisture meter around the light at haul-out will tell you.

Wipe the area dry and check again after a day. A dry, clean area is what you want. Any active drip is a reason to call a pro and plan a haul-out.

On surface-mount lights, the screws and wire hole are the leak paths. From inside, look where the wire comes through the transom for water stains or wet core. From outside (a dinghy, the swim platform or when hauled), look for cracked sealant around the light and screw heads. Installers usually put sealant in each screw hole and a thin bead around the light's edge; if yours has cracked or pulled away, reseal with the sealant your light maker specifies.

OceanLED warns that connections or bare cable ends left in a wet area or even briefly submerged will corrode and can let water travel into the light through its cable. Make sure every connection is above the bilge water line, secured, and protected with heat-shrink connectors or a sealed junction box. Look for green, crusty wire ends and replace corroded sections with tinned marine wire.

Each light circuit should have a fuse or breaker sized for the light and its wire, as close to the power source as practical. Look for:

• Warm, discolored or melted fuse holders and terminals
• Loose crimps at the controller or driver
• A controller tucked into a damp, unventilated space where it can overheat

With the lights on, measure voltage at the controller. Low voltage can cause flicker, dimming or color shifts. See our wiring and fuse panel guides for the basics.

Metal-bodied lights, especially bronze through-hulls, are underwater metal fittings like any other. Many makers require a bonding wire from the light's bonding terminal to the boat's bonding system so the anodes protect it; some polymer-bodied lights don't need bonding. Follow your manual. Check that any bonding wire is attached, tight and not corroded. Signs of trouble on the outside include paint blistering or flaking around the light, pink or pitted bronze, and heavy white powder. A light that corrodes quickly may point to stray current or a bonding problem elsewhere on the boat; see our bonding and anode guides.

Growth on the lens cuts light output fast. OceanLED says growth can noticeably dim a light in just a few weeks and recommends cleaning the lens at least monthly with a soft boat brush. When the boat is in the water, a gentle brush from the swim platform or by a diver does the job.

For barnacles and heavy growth:

• Use a plastic scraper with moderate pressure, never a metal scraper or wire brush
• Keep the lens wet while you work; OceanLED says never scrape a dry lens
• Don't use solvents, acetone, thinners, fuel, brake cleaner, strong degreasers or harsh citrus or caustic cleaners; they can damage lens coatings and seals
• Don't aim a pressure washer at the lens or bezel; OceanLED says it can damage seals and void the warranty

Shadow-Caster suggests regular light brushing so growth stays minimal, and for staining on its own housings recommends a naval-jelly rust remover used per its label. Don't assume another brand allows that; check your own maker's approved cleaners first.

Never paint antifouling or any coating over the lens. OceanLED does not recommend bottom paint or antifouling on the light face and asks owners to contact it before painting the bezel, and says aftermarket "antifoul for lights" coatings are not approved. Other makers have different rules for painting around metal housings, so read your manual. Mask the lenses with tape before the yard sands or paints the bottom, and remove the tape right after.

Every time the boat is hauled:

• Look closely at each lens for cracks, chips or water inside
• Check the sealant around through-hull flanges and surface-mount lights
• Check mounting screws and fasteners for corrosion; they should be marine-grade stainless or whatever your maker specifies
• Test each light briefly. Many underwater lights depend on water to stay cool, so only run them for the short time your manual allows when they're out of the water. Shadow-Caster's lights, for example, have thermal protection that dims them when hot

Work from simple to complex:

• All lights dead: check the switch, controller, fuse or breaker and power to the controller
• One light dead: check its connection at the controller or junction, then the cable for damage
• Dim: clean the lens first; growth is the most common cause. Then check voltage
• Flickering or color shifting: loose or corroded connections, low voltage, or water in the cable or light
• Fogging or water inside the lens: the seal has failed. The light needs repair or replacement, which usually means a haul-out

Replacing or resealing a through-hull light usually means hauling the boat, unless your light is a design where the light unit can be swapped from inside while a sealed outer housing stays in the hull, as some makers offer. Even then, follow the manual exactly. Never take out a housing or loosen its nut afloat. Drilling new holes below the waterline is a job for a yard or experienced installer.

If the boat stays in the water, keep the bilge dry around light housings and check them during winter visits. If hauled, clean growth off the lenses while it is still wet and soft, then let everything dry. Turn the light circuit off at its breaker for the season.