How to Use Solderstick Wire Connectors: Step-by-Step Guide

Solderstick connectors are solder seal connectors, and knowing how to use them properly is the difference between a splice that lasts the life of the vehicle and one that fails on a corrugated track six months later. The good news is that the method is simple: strip, join, centre, heat, cool, check. You do not need a soldering iron or a crimp tool, just wire strippers and a heat gun.

This guide walks you through each step for 12V and 24V wiring on a 4x4, car, caravan, trailer or boat, along with the mistakes that cause most bad joins and how to check your work. If you are new to these connectors, our guide to what a Solderstick is and how it works explains what is inside the tube.

Quick answer: to use a Solderstick:

• Disconnect the battery negative, then strip the ends of both wires.
• Join the bare ends (overlap, or twist them together) and slide the connector so the solder ring sits over the middle of the join.
• Heat with a heat gun, moving it around the tube, until the solder melts and flows into the strands and both end rings melt and seal.
• Leave it alone until it cools, then check through the clear tube that the solder has flowed and both ends are sealed.

What you need before you start

The kit list is short, which is one of the reasons people choose them in the first place.

• Solderstick connectors in the right size. White for 0.25 to 0.34mm2, red for 0.5 to 1.0mm2, blue for 1.5 to 2.5mm2, yellow for 4.0 to 6.0mm2. See our colour chart and sizing guide if you are unsure.
• Wire strippers. A pair that matches your wire size, so you remove the insulation without cutting strands.
• A heat gun. This is the recommended heat source. It heats the tube evenly and does not leave soot.
• Side cutters for trimming wire ends neatly.
• Cable ties or tape to support the wire either side of the finished join.

Before you cut anything, confirm the wire is the right size for the load and the circuit has the right fuse. A connector does not fix undersized cable. Our 12V wire gauge guide covers how to size cable for the current and run length.

Safety first: isolate the circuit

Always work with the circuit isolated. On a vehicle, caravan or boat, disconnect the battery negative terminal before you start. If there is a dual battery system, isolate the auxiliary battery as well, because a second battery can keep a circuit live even with the main battery disconnected. Our dual battery guide explains how those systems are usually wired.

A few other rules hold for every job:

• Solderstick connectors are for low-voltage work only: 12V and 24V automotive, marine, caravan, solar DC, low-voltage garden lighting and electronics. Never use them on 230/240V mains. In Australia, fixed mains wiring must be done by a licensed electrician.
• For battery cables and anything heavier than 6mm2, use crimped or soldered lugs, not splice connectors.
• A heat gun gets hot enough to burn skin and melt nearby plastics. Keep it away from fuel lines, plastic trims and the wiring loom you are not working on, and put it down on its stand, nozzle up.

How to use Solderstick connectors, step by step

Here is the full method. It works the same way for every size of connector.

Step 1: Choose the right connector

Match the connector colour to the conductor size of your wire in mm2 or AWG. Do not go by the overall cable diameter on the packet: auto cable sold in Australia is often labelled by its overall size, and Narva's 4mm single core cable, for example, has a conductor of about 1.85mm2, which is a blue connector. If you are joining two different sizes, see the section on mixed sizes below.

Step 2: Strip the wire ends

Strip enough insulation from each wire that the bare copper of both ends will sit under the solder ring, with the insulation reaching into the sealing rings at each end. A simple way to judge it: hold the connector next to the wire before you strip, and make sure the bare section will not extend past the coloured rings. Cut off any frayed or green, corroded copper first so you are soldering clean wire.

Step 3: Join the wires

There are two common ways to prepare the wires, covered in more detail below:

• Overlap: push the bare ends in from opposite ends of the tube so they overlap side by side under the solder ring.
• Twist: slide the connector over one wire first, then twist the two bare ends together, and slide the connector back over the twist.

Either way, keep the strands tidy. A loose strand that sticks out sideways can push through the tube as it shrinks.

Step 4: Centre the solder ring

Position the connector so the solder ring sits over the middle of the bare join and each sealing ring sits over insulation, not bare copper. This is the single most important step. If the solder ring is off to one side, one wire will be soldered and the other will only be touching.

Step 5: Heat the centre until the solder flows

Hold the heat gun so the airflow hits the middle of the tube and keep it moving around the connector, or rotate the wire, so the tube heats evenly on all sides. The tube will start to shrink first. Keep going until the solder band melts, loses its shape and flows into the strands of both wires.

Step 6: Seal the ends

Move the heat out to each end in turn until the tube has shrunk tight and the coloured rings have melted against the insulation. You will often see a small amount of adhesive appear at the ends. That is a sign the seal has formed.

Step 7: Let it cool before you move it

Take the heat away and leave the join alone until it has cooled. Moving or bending the wires while the solder is still molten can disturb the joint as it sets. Do not pull on it to test it while it is warm.

Step 8: Inspect the join

Check the join through the clear tube using the checklist further down. If it passes, support the wire and reconnect the battery. If not, cut it out and do it again with a new connector.

Overlap or twist: how to join the wires

Both methods work. The best choice depends on where you are working and how much slack you have.

A twist gives the wires some mechanical grip before the solder sets, which many people prefer. The overlap method gives a neater, slimmer join and is easier when you are working under a dash or behind a bumper with only a short tail of wire to work with.

Joining mixed sizes and more than two wires

Solderstick connectors are designed for a splice between wires of a similar size, but real wiring jobs are rarely that tidy.

Two different wire sizes

Choose the connector that suits the larger wire, then check the tube will shrink down far enough to seal the smaller wire. If the smaller wire falls well below the range of that colour, the end ring may not grip it properly. A twist join helps here because it bulks up the joint and keeps the thin wire in the solder.

Three wires (a tap or a Y-split)

When you are splitting one feed into two, such as feeding two spotlights from one wire, bring the two wires in from one end and the single wire from the other, or twist all three ends together. The combined bundle has to fit inside the tube and the solder has to reach every strand, which often means going up one connector size. Check the end with two wires has sealed all the way around, because the gap between the two insulations is where a seal is most likely to leak.

If you are regularly joining several wires at one point, a proper junction, such as a sealed distribution block or a fused distribution panel, is usually a neater and more serviceable answer than a cluster of splices.

Heat gun technique for Solderstick connectors

A heat gun is the recommended way to heat these connectors. It produces a broad stream of hot air that wraps around the tube, so the solder melts evenly and the tube shrinks without scorching. Keep the nozzle moving and a short distance from the tube rather than touching it, and use a reflector nozzle if your gun has one, because it directs heat around the back of the connector.

A lighter or gas torch puts a small, very hot flame on one side of the tube. That tends to scorch or blister the tube before the solder on the far side has melted, and it leaves soot that makes the join hard to inspect. Treat a lighter as a last resort for a roadside repair, and if you have to use one, keep the flame moving and use the hot air above the tip rather than the flame itself.

A cordless or 12V-powered heat gun is worth carrying if you do a lot of remote travel. Our first off-road trip checklist covers the rest of a basic touring tool kit.

How to check a Solderstick join

The clear tube lets you inspect the join without cutting it open. Look for these signs:

• Solder fully flowed. The band has lost its neat ring shape and has run into the strands of both wires.
• Both wires in the solder. You can see both bare ends sitting in the solder zone.
• Tube fully shrunk. Tight along its whole length with no loose sections.
• Both ends sealed. The coloured rings have melted and gripped the insulation all the way around.
• No damage. No cracks, splits, charring or strands pushing through the tube.

Once it has cooled, a gentle tug on each side confirms the solder has bonded. If you have a multimeter, a continuity check or a voltage check under load once the circuit is reconnected is a good final test.

Common Solderstick mistakes and fixes

Most bad joins come down to a handful of causes.

Once a Solderstick has been heated it cannot be reopened, so any fix that involves the inside of the join means cutting it out and starting again. Keep a few spares of each size for exactly this reason.

Supporting and protecting the finished join

Any soldered join makes the wire stiff where the solder stops. If the wire flexes or vibrates right at that point, the copper can fatigue over time. Marine and automotive wiring guidance generally says to support soldered joints so the conductor does not flex at the joint. In practice that means:

• Cable tie or tape the wire to the loom or a solid mount either side of the join, so the join itself is not carrying any movement.
• Leave a little slack so the wire is never pulled tight across the join.
• Run exposed sections through split conduit and keep them clear of sharp edges, exhaust parts and anything that moves, such as steering components or suspension.
• On a trailer, keep joins up off the bottom of the drawbar where stones and water hit hardest. Our off-road towing guide covers trailer setups in more detail.

For wiring that is constantly flexing, such as a run to a tailgate or a hinged panel, place the join on the fixed side of the hinge, not in the flexing section.

Which should you use?

• If you are splicing a 12V or 24V wire between 0.25mm2 and 6.0mm2 and want it sealed, use Solderstick connectors in the colour that matches the conductor size.
• If you have plenty of slack and want extra grip before heating, use the twist method. If you have a short tail or a tight space, use the overlap method.
• If you are splitting one wire into two, go up a connector size if the bundle will not fit, or use a distribution block for several wires.
• If you have a heat gun, use it. If you only have a lighter, treat the join as temporary and redo it with a heat gun when you can.
• If you are working on battery cable or anything over 6mm2, use crimped or soldered lugs and adhesive-lined heat shrink instead.
• If the job involves 230/240V mains, stop and call a licensed electrician.

Frequently asked questions

How long do you heat a solder seal connector?

Heat it until you see the solder band melt and flow into the wires and both end rings seal, not for a set time. Small white and red connectors melt quickly, while larger yellow connectors on thicker wire take noticeably longer because there is more copper to warm up.

Do you twist wires before using Solderstick connectors?

You can, but you do not have to. Twisting gives extra mechanical grip before the solder sets, while overlapping the ends side by side gives a slimmer join and works well in tight spots. Both work as long as both wire ends sit under the solder ring.

How much wire do you strip for a solder seal connector?

Strip enough that both bare ends sit under the solder ring while the insulation reaches the sealing rings. Hold the connector against the wire as a guide before stripping, so the bare copper will not extend past the coloured rings.

Can you use a lighter on Solderstick connectors?

Only as a last resort. A lighter can scorch the tube before the solder melts and leaves soot that hides the join. A heat gun is the recommended heat source.

How do you know if a Solderstick join worked?

Look through the clear tube: the solder should have melted and flowed into both wires, the tube should be tight along its length and both coloured end rings should have melted onto the insulation. If the solder still looks like a ring, apply more heat.

Can you redo a Solderstick join?

You can reheat one that has not fully flowed or sealed, but you cannot open it up once it has shrunk. If the wires are not positioned correctly, cut the join out and fit a new connector.

Do I need to disconnect the battery to use Solderstick connectors?

Yes. Disconnect the battery negative before cutting or joining any wire, and isolate any auxiliary battery as well. It prevents shorts and protects the vehicle's electronics.

What to use

For most people, an assorted kit is the easiest way to always have the right size on hand. Every Solderstick kit includes all four colours, and the connectors are ISO 9001 and CE certified and IP67 rated.

• 50PCS kit (10 white, 22 red, 13 blue, 5 yellow): a good glovebox or recovery bag kit for roadside repairs.
• 100PCS kit (25 white, 35 red, 30 blue, 10 yellow): suits an accessory install with spares.
• 250PCS kit (40 white, 100 red, 90 blue, 20 yellow): for a full caravan, trailer or 4x4 wiring job.
• 500PCS kit (80 white, 200 red, 180 blue, 40 yellow): for workshops and regular users.
• Bulk 100 packs of one colour, if you use mostly one size.
• Adhesive-lined dual wall heat shrink for battery lugs, bundling spliced wires together and adding extra strain relief.

Orders ship within Australia by Express Australia Post, with free express shipping Australia wide. Orders placed by 1pm are dispatched the same day.