Wire harness connector with mixed-gauge colored wires
Solder versus crimp repairs.

Personally, I solder very little. I save solder projects for repairs that have to be kept small or, in the field, maybe I don't have the correct terminal to make a repair and am forced to reuse the original.

Solder can be a good way to attach wires that are very different in diameter.

Soldering is about controlling heat.

⚠️ Caution

Too much heat travelling up the circuit that you're soldering can cause solder to travel up wires, making sections of the circuit stiff with solid solder. This will cause stress points and future wire breaks from vibration.

Crimp repairs are very reliable and often time superior.

See Also ↗
Wire Repair
Remove and Install Terminals, Identify Corrosion. Power and ground terminals are the most likely to corrode.
Test Leads

Test Lead Parts

Test lead parts laid out: red and black silicone wire, banana plugs, and boots

Don't forget to install the connector boots on the wire before soldering the plugs.

Notice the difference in the boots between male and female 4mm plugs. The boots for the male plugs have flex relief slots.

Red connector boot installed on wire before soldering
Cross-section of a male 4mm banana plug showing the wire pocket

Strip just enough insulation off the wire to allow the conductors to fill the pocket of the plug. You do not want conductors to be exposed out the back side of the plug.

Avoid twisting the conductors. It only makes the wire bulkier.

Finished soldered plug with solder flowed through the conductors

Make sure solder flows through the conductors and securely attaches the wires to the plug.

Solder all 4 plugs. Slide each plug boot in place. It may be helpful to slightly heat each boot.

High-Current Test Light

Test Light Parts

High-current test light parts laid out: handle, magnet, bulbs, bulb holders, and hardware

Assemble the bulb holder.

The bulb holders need to be wired in parallel. The bulbs ground through the bulb holder. Both holders will be bolted to the same ground. Both power wires need to be soldered to the same plug.

Don't forget to install the plug boot. The boots without flex relief slots work better on the female plugs.

Both positive wires from the center of the bulb holders will be soldered to a single 4mm female banana socket.

Two bulb holders wired in parallel, ready to be soldered to a single plug

Trim only the necessary amount of insulation.

Avoid twisting the two wires together. This only make the wire end bulkier.

Two wire ends stripped and twisted together, ready to solder into a socket

Solder the female 4mm socket. Make sure the solder penetrates the conductors and secures the wire to the socket.

Slightly heat and slide the socket boot in place.

Assemble the ground wire

Solder the single ground wire to a 4mm female socket.

Slightly warm and install the socket boot. The boots without flex relief slots work better on the female plugs.

Avoid twisting the conductors before inserting them into the splice.

Crimp the #8 eyelet with the proper tool.

Ring terminal, connector boot, and 4mm socket laid out before crimping
⚠️ Be Sure to Use the Insulated Crimp Die

Don't use the non-insulated tool on an insulated splice. The non-insulated die will puncture the insulation. Corrosion will damage this connection.

Crimp tool jaws with the insulated die circled
A fork terminal showing where a non-insulated die punctured the insulation — marked as a mistake to avoid

Heat the eyelet to seal:

Sealed eyelet with heat-shrink boot, glue extrusion and conductor coverage circled

Assemble Bulb Holders

Pass the 8x32 screw through the first hole in the handle from the bottom.

Install both bulb holders, the ground wire eyelet, and 8x32 nut. This is the parallel ground connection.

Both bulb holders mounted to the aluminum handle with the ground wire bolted between them

Assemble Magnet and P-Clamp

Insert threaded post of magnet through second hole.

Secure P-clamp around all three wires.

Install P-clamp, washer, lock washer, and nut.

Completed high-current test light handle with magnet base and P-clamp securing all three wires