How to Solder Wires With a Soldering Iron

Use your wire stripper (on the correct gauge) or a sharp utility knife to cleanly remove around 1/2-inch to 3/4-inch of the colored plastic insulation coating from each of your wires. This is the right amount to strip to ensure you can solder correctly without using too much heat shrink tubing in the next step.

Take care not to damage the wires underneath—using the correct gauge wire cutting will help here. Scraping the plating exposes copper wires to oxidation, and you can compromise the electrical connections.

Next, grab your flexible plastic tubing designed to fit snugly over the wires. Make sure you buy the proper-sized tubing. Go too large, and it won’t shrink down to fit and insulate properly after the soldering. It shrinks at least 50% when you apply heat. 

Cut a length that covers the splice plus 1/2-inch on either end. Slip the tubing over one of the wires. For now, slide it down the wire so that it rests a safe distance away from the exposed area you will solder later.

Twist the wires from both sections until they interlock to help reduce cracking in the solder joint and improve its integrity. They should twist tight enough that they are smaller in diameter than the heat shrink tubing. Don’t overdo it, though—this can make it difficult for the soldering action to penetrate.

Rub a little rosin flux paste across the wire to cover the join completely. This helps to pull the solder into the connecting wire strands. 

To activate the rosin flux, touch the soldering iron tip close to the wire for a couple of seconds. The heat will cause the rosin flux to melt. When it starts smoking, this means the flux is activated.

If you’ve used the iron before, clean the iron’s tip with a damp sponge to remove any lingering oxidation residue. A clean tip will maximize conductivity and produce a clean joint. If you’ve purchased a few soldering iron for this project, you can skip this step.

Next up: The fun part. Grab your protective gloves and goggles before handling the soldering iron.

1. Turn on the soldering iron and unroll around four to six inches of solder ready to use.

2. Keep the heated soldering iron in its designated stable cradle or stand when not in use to prevent any scorch damage or fire risk. Turn it off if you need to leave it unattended at any point and only grab the iron by the insulated handle.

3. The solder and the solder tip should match the diameter of the existing wire as closely as possible.

4. Press the tip of the iron against the wire meshed strands.

5. Hold firmly for a few seconds to allow the solder to melt onto the iron.

6. Touching the solder lightly against the joint should immediately combine the wire strands.

Give yourself (and the solder iron) a moment to rest. Allow the solder to cool and solidify for a couple of minutes. Leaving the wires undisturbed while it’s drying promotes a solid connection.

Pull the heat shrink tubing over the soldered connection. Let it overlap with the original insulating tubing by at least 1/4 inch on either side, ensuring all parts of the exposed wire are covered. 

Finally, grab your heat gun. Use it to shrink the insulating tubing around the wire. If you don’t have a heat gun, you can run a lighter close to the tubing instead.