How I Solder a Wire Splice – Tinning and Heat-Shrink Tubing

This is the method I usually use when soldering two wires together. My aim is to make a splice that is straightforward to produce, mechanically stable while I solder it and well protected afterwards.

A full YouTube video of the entire process is included at the end of the article.

Pre-tinning the wire ends

I usually pre-tin the wire ends before making the splice itself. This makes it easier to see that the copper accepts the solder, and the final soldering step is generally quicker afterwards.

I put a small amount of solder on the soldering-iron tip to transfer heat effectively into the conductor. I then feed solder from the opposite side of the wire. Once the conductor is hot enough, the solder flows in between the copper strands.

Stripped yellow wire end with exposed copper strands before pre-tinning — The stripped wire end before pre-tinning.

Soldering iron heating the copper strands in a yellow wire end — The soldering iron heats the conductor. A small amount of solder on the tip improves heat transfer.

Solder being fed from the opposite side of the heated wire end — The solder is fed from the opposite side while the conductor is kept hot.

Pre-tinned wire end with solder drawn in between the copper strands — The finished pre-tinned wire end.

Light mechanical locking

Before soldering the wire ends together, I normally make a light mechanical lock by twisting the conductors together.

The aim is not to make a large or complicated splice, but to keep the wire ends in position while I solder them. This is particularly useful in cramped engine bays, where using a soldering stand or another aid is not always practical.

In some situations, a parallel splice may be a better option, for example when there is very little room to strip the wires and lay the conductors end to end. I will return to that in a separate article.

Pre-tinned conductors from a black and a yellow wire twisted together to form a light mechanical lock — The two pre-tinned conductors are twisted together so that the splice remains in position during soldering.

Soldering the splice

Once the splice is mechanically stable, I begin the soldering itself.

I again put a small amount of solder on the soldering-iron tip to transfer heat effectively into the splice. I feed the solder from the opposite side.

Once the copper is hot enough, capillary action draws the solder in between the conductors. The aim is for the solder to spread through the splice, rather than merely coating the outside.

Soldering iron heating the mechanically locked wire splice from below — The mechanically locked splice is heated with the soldering iron.

Solder being fed from above while the wire splice is heated from below with the soldering iron — The solder is fed from the side opposite the soldering iron.

Molten solder flowing in between the copper strands in the wire splice — Once the conductors are hot enough, the solder flows into the splice.

Wire splice being kept hot while the solder spreads between the conductors — The splice is kept hot long enough for the solder to spread between the conductors.

Finished soldered splice between a black and a yellow wire — The finished soldered wire splice after cooling.

Finishing work

Once the splice has been soldered, I feel for sharp strand ends or uneven areas.

If a copper strand is protruding, I carefully trim it off. This makes the surface smoother and reduces the risk of a sharp edge later damaging the heat-shrink tubing.

Fingers checking the soldered wire splice for sharp strand ends — I check the splice for sharp strand ends and uneven areas.

Side cutters trimming a sharp copper strand from the soldered wire splice — A protruding copper strand is carefully trimmed off.

Heat-shrink tubing

Finally, I slide the heat-shrink tubing over the splice and shrink it with a heat gun.

I prefer a heat gun to a lighter or an open flame. It gives me better control over the heating and makes it easier to shrink the tubing evenly without overheating the wire or the heat-shrink tubing.

Black heat-shrink tubing being slid over the cooled wire splice — The heat-shrink tubing is centred over the cooled splice.

Heat gun evenly shrinking black heat-shrink tubing around the wire splice — The heat-shrink tubing is heated evenly with a heat gun.

Finished wire splice protected by evenly shrunk black heat-shrink tubing — The finished wire splice with the heat-shrink tubing in place.

Result

The finished splice should be mechanically neat, well soldered and free from sharp edges beneath the heat-shrink tubing.

This is the method I usually use for smaller wire repairs where soldering is a suitable solution.

Video

Watch the video on YouTube