Guide
How to Solder Wire (Wire-to-Wire Joints)
Published:
TL;DR
- Strip and twist the wires together mechanically before you solder. Solder holds a joint, it isn't the joint itself.
- Tin each wire separately first, then join the two tinned ends with heat.
- Slide heat-shrink tubing onto one wire before you start, you can't add it after the joint is made.
- Match iron wattage to wire gauge: thin signal wire needs less heat than thick automotive-gauge wire.
Prepare the wires
Strip 10-15mm of insulation from each wire end. If you're joining two solid wires, twist the bare strands together first so there's a mechanical connection before solder ever touches them, solder should reinforce a joint, not be the only thing holding it together.
If you'll need to insulate the joint afterwards, slide a length of heat-shrink tubing onto one of the wires now, before you solder. It's much harder to add once the joint is made.
Tin each wire, then join them
Heat each wire end and flow a thin coat of solder into the strands, this is tinning, and it's easier to do on each wire separately than trying to solder two bare, untinned ends together at once.
Twist or hook the two tinned ends together, then apply the iron to the joint until both tinned surfaces melt and flow into one another. Hold still while it cools.
Insulate the joint
Once the joint has cooled, slide the heat-shrink tubing over it and apply heat (a heat gun, or carefully with the side of the soldering iron) until it shrinks tight. Electrical tape works as a fallback but heat-shrink gives a more durable, vibration-resistant result.
Matching wattage to wire gauge
Thin signal or data wire solders fine on a low-wattage iron. Thicker gauge wire, like automotive wiring, pulls heat away faster and needs more wattage to solder quickly, a low-wattage iron will dwell too long trying to get the joint hot enough, risking melted insulation nearby.