Boat Trailer Wiring for Cairns Boat Ramps

This guide is for Cairns boaties who tow to the Trinity Inlet ramps, Yorkeys Knob or the river ramps and keep finding a dead tail light on the way home. It covers where trailer wiring fails, how to set up a trailer that copes with regular dunking, and the Queensland rules you need to keep in mind.

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Where Cairns boaties launch

Cairns has a good spread of public ramps, and each one treats your trailer a little differently. Cairns Regional Council lists ramps in Trinity Inlet off Trawler Base Road, Tingira Street, Smith Street and Redbank Road, plus ramps at Yorkeys Knob, Palm Cove and Stratford. A few that local trailers see often:

• Tingira Street, Portsmith. Launches into Smiths Creek and has a floating walkway and pontoon. The walkway was added on the downstream side in 2016.
• Fearnley Street, Portsmith. Launches into Trinity Inlet, with a floating walkway.
• Yorkeys Knob. A six-lane ramp with three floating walkways that opened in September 2023, with parking for 135 car-and-trailer combinations.
• Stratford, off the Captain Cook Highway, for Barron River access.
• Palm Cove, which the council describes as a calm-weather launching spot.

Tides, mud and long reverses

Trinity Inlet, Smiths Creek and the coastal ramps are all tidal. On a low tide you may need to back further down to float the boat off, which puts the tail lights and the rear of the harness deeper into salt water than you planned. Check the Maritime Safety Queensland tide tables for Cairns before you go, so you can pick a launch and retrieve time that suits your ramp.

A long reverse also means more chance of the trailer plug dragging, or the harness snagging on rollers when the boat comes back on. Most of the trailer faults that turn up after a day on the water start with one of those two things.

What salt water does to trailer lights

Standard filament trailer lamps are not built to be dunked. A warm globe hitting cool water can crack, and any water that gets past the lens seal starts working on the globe holder and contacts straight away. The fault often comes and goes: dead at the ramp, working again in the driveway once it dries out.

Sealed LED lamps sold as submersible are the usual upgrade for a boat trailer. They have no filament to break and no holder to corrode, and fully potted units keep water out of the electronics. The weak points then move to the joins, the earth and the plug, so that is where your effort should go.

If a light has already dropped out, our guide on why trailer lights stop working walks through tracing the fault circuit by circuit.

Setting up a trailer that copes

The best boat trailer wiring has as few joins as possible below the waterline. Run the harness along the top of the frame or inside the drawbar, and keep it well away from the rollers, skids and winch strap. Bring the joins forward to a sealed junction point near the drawbar, which stays drier than the back of the trailer.

Where wires must be joined, use adhesive-lined heat-shrink connectors, crimped with the right tool and shrunk until the glue seals both ends. Tape and twisted wire won't last long on a trailer that sees salt water every weekend. Our guide to crimping wire connectors shows how to get a joint that holds.

• Run a dedicated earth wire to each lamp instead of relying on the lamp bolting to the frame.
• Use tinned cable if you are rewiring, as it resists corrosion creeping along the strands.
• Leave a drip loop before each lamp so water runs off rather than into the connection.
• Secure the harness with clips or ties every so often so it can't sag into the rollers.

Plug habits at the ramp

Unplug the trailer before the lights go under water and plug it back in once you are clear of the ramp. With the plug disconnected, the lamps are off and cooler when they get wet, and nothing is live. Hang the plug over the drawbar or in a holder so it doesn't scrape along the concrete and fill with grit and salt.

Most boat trailers use a 7-pin flat plug. If yours is cracked, loose or green inside, replace it rather than cleaning it for the fifth time. Our guide on wiring a 7-pin trailer plug has the standard pin layout.

Take care at the water's edge while you do this. Queensland's environment department warns that crocodiles can be in any north Queensland waterway, even without a sign, and that fish scraps and bait left at ramps attract them. Do your plug and light checks well back from the water, not standing in it.

Queensland towing rules to keep in mind

The Queensland Government's towing vehicles and trailers page says your car needs electrical sockets for the trailer lights and that the trailer must have a lit rear number plate that isn't obscured. It also notes that towbars and couplings must not cover your car's number plate or rear lights when the trailer isn't connected, and it singles out boat trailers for regular checks of wheel bearings, suspension and brakes.

Brakes depend on the trailer's mass. Transport and Main Roads' safe towing guide says a single-axle trailer with a gross trailer mass of 750 kg or less doesn't need brakes. Heavier trailers up to 2000 kg need brakes on at least one axle, and above 2000 kg they need brakes on all wheels, operable from the driver's seat, plus a breakaway system that applies the brakes if the trailer comes off. Once the motor, fuel, ice and safety gear are on board, a rig can weigh more than you expect, so use a public weighbridge if you are unsure.

These are summaries only. Rules change, so check the current requirements with Transport and Main Roads before you buy, modify or register a trailer.

After the trip, and when to get help

Hose the trailer with fresh water when you get home, including the lamps, plug and the underside of the drawbar where the harness runs. Let the plug dry before you put a cover on it. Every month or so, clean the plug pins and coat them with a water-displacing spray.

Do a full light check with a helper before every trip: tails, brake lights, both indicators and the number plate light. If the harness is corroded along its length, a complete rewire with sealed lamps usually costs less than chasing one fault after another. Auto electricians around Portsmith and the Northern Beaches see a lot of boat trailers, and many will come to you.

Parts for this job

Order quality parts online from Ozautoelectrics, dispatched Australia-wide.

Get it done: get a quoteDo it yourself: shop submersible LED trailer lights

Get it done: get a quoteDo it yourself: shop 7-pin flat trailer plugs

Get it done: get a quoteDo it yourself: shop heat shrink connectors

Get it done: get a quoteDo it yourself: shop trailer cables

Questions Cairns drivers ask

Do I need brakes on my boat trailer in Queensland?

It depends on the trailer's mass. Transport and Main Roads says a single-axle trailer with a gross trailer mass of 750 kg or less doesn't need brakes. Above that, brakes are required, and over 2000 kg they are needed on all wheels with a breakaway system. Check the compliance plate and the current TMR rules, and weigh the loaded rig if you are not sure.

Why do my trailer lights work at home but fail at the Tingira Street ramp?

Usually salt water has got into a join, a lamp housing or the plug. When it is wet, the connection shorts or loses voltage, and once it dries the fault seems to disappear. Check the earths first, then open the plug and look for green or white corrosion on the pins. A multimeter will show you which circuit is losing power.

Should I unplug my trailer before backing into the water at Yorkeys Knob?

Yes, it is a good habit at any ramp. Unplugging means the lamps are off and cooler when they go under, and no circuit is live in salt water. Keep the plug off the ground while disconnected, then plug back in once you are clear of the ramp and do a quick light check before you drive off.

Are LED lights worth fitting to a Cairns boat trailer?

For a trailer that goes in salt water often, usually yes. Sealed LED lamps sold as submersible have no filament to crack and no globe holder to corrode. They won't fix a poor earth, a corroded plug or taped joins, though, so seal the connections and run proper earth wires at the same time.

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