Waterproof 12V Garden Lighting Connections: How-To Guide

Low-voltage garden lights look great the night you install them. Two wet winters later, half of them are dim or dead, and the cause is almost always the same: water in the connections. Sprinklers, wet soil, mulch and fertiliser salts are hard on copper, and a join that is taped or clipped together will corrode from the inside out.

This guide shows you how to make waterproof 12V garden lighting connections that last, how to plan the cable run so the last light is as bright as the first, and where the line sits between DIY and licensed work. It covers the extra-low-voltage side only: the cable and fittings after the transformer.

Quick answer

• Work only on the 12V side. The transformer's mains side is 230V, and any fixed mains work is for a licensed electrician.
• Join cable with sealed connectors, such as Solderstick connectors, not tape or bare twists.
• Keep joins out of standing water: lift them above the soil or put them in a sealed junction box.
• Use cable sized for the total load and the length of the run to avoid dim lights at the far end.
• Leave a loop of spare cable at each light so you can remake a join later.

Mains side vs 12V side

Photo: Irwan Rosyadi on Unsplash

A low-voltage garden lighting system has two halves. The transformer, or LED driver, takes 230V mains and turns it into 12V. Everything after it, the cable, the joins and the lights, runs at extra-low voltage.

The mains side is not DIY territory. If your transformer plugs into an existing outdoor power point, you can plug it in and unplug it like any appliance. Installing a new outdoor power point, hard-wiring a transformer, or running mains cable through the garden must be done by a licensed electrician. An electrician can also confirm the outdoor circuit is protected by an RCD.

Solderstick connectors are for the 12V side only. Never use them on 230V wiring.

12V AC or 12V DC?

Traditional garden lighting transformers put out 12V AC. Many LED systems use a driver with a 12V DC output instead. The lights are designed for one or the other, or sometimes both, so check the label on the light and the transformer before you add fittings. Solderstick connectors work the same on either; what matters is that the lights match the supply.

Check the transformer's rated output (in watts or VA) against the combined wattage of your lights, and leave some headroom. Overloading a transformer shortens its life and can trip its protection.

Why 12V garden lighting connections fail

Garden joins sit in the worst conditions of any low-voltage wiring:

• Constant moisture. Wet soil and mulch keep a join damp for weeks, not hours.
• Fertiliser and salt. Dissolved salts make water more conductive and speed up corrosion, especially near the coast.
• Movement. Garden beds get dug, spikes get bumped and cables get tugged by mowers and trimmers.
• Heat and UV. Exposed cable and joins break down in the sun.

Kit-supplied piercing connectors and twist-and-tape joins are the usual weak points in garden lighting connections. Once water gets in, the copper turns green and resistance rises until the light at the end of the run fades.

Connection methods compared

How to make waterproof garden lighting connections

1. Turn it off

Switch off and unplug the transformer before you cut or make any garden lighting connections.

2. Cut back to clean copper

If you are repairing an old join, cut it out completely and strip back until the copper is bright. Green or black strands will not take solder well and will keep corroding.

3. Pick the right size connector

Garden lighting cable is usually twin-core. Check the conductor size on the cable or its packaging and match it:

• Red: AWG 22-18, 0.5-1.0mm². Light tails and short spurs.
• Blue: AWG 16-14, 1.5-2.5mm². Typical main runs.
• Yellow: AWG 12-10, 4.0-6.0mm². Heavy main runs on larger systems.

4. Join and heat

Slide the connector over one wire, overlap or twist the strands so they sit under the solder ring, then centre the connector. Heat with a heat gun, working from the middle out, until the solder flows into the strands and the coloured rings at each end melt and seal. Let it cool before moving it.

5. Stagger and protect

On twin-core cable, offset the two joins by a few centimetres so the finished splice is slimmer. Slide a length of adhesive-lined heat shrink over both joins and shrink it for a second layer of protection and strain relief.

Where to put the joins

Solderstick connectors are rated IP67: dust tight and able to withstand temporary immersion. That is a strong seal, but a join sitting permanently in waterlogged soil is a harder test than temporary immersion. Give your garden lighting connections the best chance:

• Make joins near the light fitting, lifted just above the soil and tucked under the fitting.
• Where you must join below ground, use a sealed outdoor junction box.
• Avoid low spots where water pools after rain or irrigation.
• Keep joins away from sprinkler heads.

For more on what the IP numbers mean, see our IP rating guide, and for a closer look at the rating on these connectors, read is Solderstick waterproof.

Planning the cable run

On a 12V system, voltage drop is the main reason lights at the end of a long run are dimmer than those near the transformer. The current is higher than on mains for the same wattage, so thin cable over a long distance loses a noticeable share of the supply.

• Use a heavier main cable and lighter tails to each fitting.
• Split a long line into two shorter runs from the transformer.
• Feed the cable from the middle of a line of lights rather than one end.

Our wire gauge guide explains how load and length affect cable choice. The same principles apply in the garden as in a 4x4.

Lay cable where you are unlikely to dig, follow the light maker's instructions for burial or conduit, and record where the cable runs so you do not cut it next time you plant.

Which should you use?

• If you're joining a light's tails to the main run, use the connector that matches the main cable size, usually blue.
• If you're repairing thin LED tails, use red.
• If you're joining a heavy main run on a larger system, use yellow.
• If you want extra protection over a join in a damp spot, add adhesive-lined dual wall heat shrink.
• If the job involves the transformer's mains side, a new power point or fixed mains wiring, call a licensed electrician.

Frequently asked questions

How do you waterproof low-voltage garden light connections?

Use a sealed connector that bonds and seals the wire, such as a Solderstick connector or a crimp covered with adhesive-lined heat shrink. Then keep the join out of standing water by lifting it near the fitting or putting it in a sealed junction box.

Can I install 12V garden lighting myself?

The 12V cable and lights after a plug-in transformer are generally DIY. Installing a new outdoor power point or hard-wiring a transformer is mains work and must be done by a licensed electrician.

Why are the lights at the end of my garden run dim?

That is usually voltage drop from a long run of thin cable, or a corroded connection partway along. Check the joins first, then consider heavier cable or splitting the run.

Can I bury solder seal connectors?

They are rated IP67, which covers temporary immersion. For joins that would sit permanently in wet soil, lift them above ground near the fitting or put them in a sealed junction box.

Do Solderstick connectors work on 12V AC garden lighting?

Yes. The connector joins and seals the wire regardless of whether the 12V supply is AC or DC. They must not be used on the 230V side of the transformer.

What to use

For a typical home garden system, the 50PCS Solderstick kit suits a small system or a round of repairs. Larger landscapes suit the 100PCS kit, or a bulk 100-pack bag in the colour that matches your cable. Add adhesive-lined dual wall heat shrink for a second seal over joins in damp beds. If you also want to tidy up the lighting on your boat or trailer, see our guide on how to wire trailer lights. Free express shipping Australia wide, with orders placed by 1pm dispatched the same day.