Boat Trailer Wiring for Bunbury and Busselton Ramps

This guide is for anyone who launches a boat around Bunbury, the Leschenault Estuary or Geographe Bay. It covers why trailer lights fail so often here, how to wire a trailer that survives salt water, a simple routine for the ramp, and the WA rules on trailer lights and brakes you should check.

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Where local trailers get wet

The Bunbury region has plenty of public ramps. WA's transport department lists regional boat ramps including Casuarina Boat Harbour, Stirling Street, the power boat club and Turkey Point in Bunbury, Ridley Place in Australind, and Port Geographe, Dolphin Road, Georgette Street, Newtown Beach, Scout Road and Wonnerup around Busselton. Further west, Dunsborough has ramps at Finlayson Street and Elmore Street.

Each launch site is a little different. A ramp inside a sheltered harbour may let you launch without dunking the hubs, while a beach-side ramp on Geographe Bay may push the whole trailer under. Estuary ramps are shallower but the water is still salty. Either way, the back of the trailer, where the lights and their wiring sit, spends time underwater.

What salt water does to wiring

Salt water conducts electricity and attacks copper, steel and brass. Once it gets into a lamp housing or a joint, it starts corroding the contacts. Current flowing through wet contacts speeds that up. Copper wire then turns black or green inside the insulation, sometimes a long way from the original leak.

The symptoms are familiar: one side of the trailer stops working, indicators flash fast, brake lights glow when the tail lights are on, or everything works on the driveway but fails after the first launch. Most of these come back to three places: the lamps, the plug and the earth. Our guide on why trailer lights stop working walks through the fault finding.

Building a trailer that survives

If your trailer lights keep failing, a rewire with marine-friendly parts is usually better than patching. Key points:

• Use sealed, submersible LED lamps. They run cool, so cold water doesn't crack them, and they have no globes to corrode.
• Use tinned copper cable where you can. The tin coating resists corrosion far better than bare copper.
• Run a dedicated earth wire to each lamp rather than relying on the trailer frame, especially on galvanised trailers.
• Keep joints to a minimum. Where you need one, use adhesive-lined heat shrink connectors.
• Run cable inside the drawbar or in conduit, away from the winch strap, rollers and sharp edges.
• Fit a sealed junction box near the drawbar if the trailer has several circuits, and pack it with dielectric grease.

The plug and socket

The plug is the weak point on most boat trailers. It hangs near the ground, collects sand and salt, and is often left sitting in a puddle at the ramp. Check the pins for green crust before every trip, and clean them with a small brush or contact cleaner. A light coat of dielectric grease helps keep moisture out. Make sure the car's socket has a spring-loaded cover that closes properly.

If you're rewiring the plug, take care with the pin layout. Our guide on how to wire a 7-pin trailer plug shows the standard arrangement. Many small boat trailers use a flat 7-pin plug, while larger rigs with electric brakes often use a round 7-pin or 12-pin plug.

A simple ramp routine

A few habits at the ramp add years to trailer wiring. Before you back down, unplug the trailer so no current flows through wet contacts, and hang the plug somewhere off the ground. After you retrieve the boat, let the trailer drain for a minute before plugging back in. Check that every light works before you drive off.

At home, hose the whole trailer down with fresh water, including the lamp housings, the plug and the underside of the drawbar. The Road Safety Commission's towing advice also recommends flushing boat trailer brakes with fresh water after use and testing all trailer lights before you leave.

Brakes and the WA rules

Larger boats often need a braked trailer. WA's transport department sets out the requirements in its Safe Towing bulletin (IB-107). In summary, trailers with a gross trailer mass over 750 kg need brakes. Up to 2000 kg, brakes on at least one axle are enough and over-ride brakes are allowed. Over 2000 kg, all wheels must be braked, the brakes must be operated from the driver's seat and a breakaway system is required.

The same bulletin says trailer wiring, lighting and reflectors must meet the Australian Design Rules, and the tow vehicle needs sockets for the trailer lights and brake connections where necessary. Electric brake magnets and wiring on a boat trailer suffer badly from salt, so if your trailer has them, inspect and rinse them after every launch. Rules change and depend on your trailer's ratings, so check the current bulletin and your compliance plate.

Finding a fault at the ramp

If a light fails when you're about to head home, start with the simplest checks. Unplug and replug the trailer, and look for sand or green crust on the pins. Check the car's fuses for the trailer circuits, as many vehicles have separate fuses for the trailer socket. If one side is dead, look at the earth wire at that lamp. If every light is dim or behaves strangely, the main earth at the plug or the drawbar is the usual suspect.

Carry a small test light or multimeter, a few spare connectors and a roll of electrical tape in the car. A temporary fix may get you home safely, but do the proper repair before the next trip.

Storage between trips

Many trailers sit on a lawn or under a carport for weeks. Salt left on the wiring keeps working the whole time. Rinse it off after every trip, store the plug inside a bag or cap, and check the lights a few days before your next outing so there's time to fix a fault. If you launch at the estuary, see our Australind page, and if you launch on Geographe Bay, our Busselton page has more local tips.

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Questions Bunbury drivers ask

Why do my boat trailer lights fail after every launch?

Salt water is getting into the lamps, plugs or joints. Old globe-type lamps crack and corrode quickly, and a poor earth makes faults worse. Switching to sealed LED lamps, tinned cable and a dedicated earth wire usually fixes it. Unplug before launching and rinse with fresh water afterwards.

Does my boat trailer need brakes in WA?

It depends on the trailer's mass. Under WA's Safe Towing bulletin, trailers with a gross trailer mass over 750 kg need brakes, and over 2000 kg they need brakes on all wheels, operated from the driver's seat, with a breakaway system. Check your trailer's compliance plate and the current bulletin.

Should I unplug my trailer before backing into the water?

Yes. Unplugging stops current flowing through wet contacts, which speeds up corrosion, and protects any older globes from cracking in cold water. Hang the plug somewhere dry while you launch. Plug back in after the trailer has drained, then check every light before driving off.

Can I use ordinary automotive cable on a boat trailer?

It will work, but it won't last as long. Bare copper corrodes once salt water gets in, and the damage can spread inside the insulation. Tinned copper cable resists corrosion much better. Combine it with sealed connectors and as few joints as possible for the most reliable result.

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