Soldering Wire Harnesses: A Preferred Automotive Wiring Connection for Your Car 


Even seasoned mechanics become agitated when working on your car’s electrical system. Intermittent difficulties, complex dashboard harnesses, and years of “fix it and forget it” remedies only worsen things. Most electrical problems are caused by a faulty connection, in our opinion. Some applications call for crimp terminals because of their efficiency and reliability. However, corrosion can develop and cause issues with the connection over time. One of the most reliable methods of repairing electronic devices is soldering. Let’s dig into more details on soldering wire harnesses.

Table of Contents

Repairing through soldering

Caption: Repairing through soldering

Tools you need for the soldering wire harnesses.

It would help if you had special tools to create a reliable automotive wiring connection through soldering.


60 to 40 rosin core solder is required for this task. In other words, it has 60% tin and 40% lead. The flux in the rosin core melts before the metal does. The melting point of this solder is around 370 degrees Fahrenheit. Fusing the wires when the flux melts and coats them will be easier. Without it, the wire gets prone to melting into a tough metal ball. 

Soldering iron

The wire is immediately heated with a soldering iron. If you fix an automobile’s wiring, you’ll need a 40 to 45-watt iron to solder the connection because a 30-watt iron will not heat the wires quickly enough.

The workbench is not the best place to do everything. Because a powerful solder gun might overheat the wire shielding or inject electric currents into a circuit, be careful while using it.

Wire strippers

Pliers or scissors are the closest analogy for wire strippers. Strippers can perform a wide range of activities, but their principal function is to remove the insulation off wires. The slotted cutting blades inside the stripper are responsible for this. When a wire is drawn through the slot, its insulator is left behind because the cutting grooves are tailored to suit various gauges of wire but not the wire’s insulation layer.

All you need is to insert the cable end into the slot on the end of the strippers and then close the jaws. Pull the wire with the jaws clamped down. As the wire is inserted into the slot, you should strip it of its insulation. Because stranded and solid wire have different diameters, each slot has two labels denoting the various sizes.

Electrical tape or PVC shrink tube

For soldered joints, shrink tubing provides the finest seal. Before soldering, carefully slide the tubing a few inches past the connection. You can use 3M Super 33 electrical tape instead of shrink tubing if that is not an option.


You also need a soldering sponge to help remove the solder residue from your soldering iron.

Process of soldering wire harness

Now, it’s time to do the work.


First, strip the shielding of the wire pieces you want to solder and cut off a quarter of an inch.


Then, twist them around each other until they are secure. Set it on one of the wires using a PVC shrink tube. For soldering, there is only one method to twist wires together: horizontally. That makes one long piece of wire. A pig-tail, where you bend the wires at a 90-degree angle from the rest of the wire, is not a good connection and will cause problems, so don’t do it.


Make a cross with the wires in the middle of the stripped section. Wrap the wires into each other. Make sure the package is well sealed. It is a good way to hook up more than one wire to a single lead.


Next, get your iron ready. Heat the tip until it steams when it gets wet, and then wipe away any old solder with a wet sponge. Tin the end of the wire after it has been cleaned. In other words, put the solder on it. Experts also say that you should put some solder on the tip because it makes the tool more conductive and speeds up the job. It is best to solder them together quickly to keep the wires from breaking.

When the soldering iron is ready, you can solder the wires together. Instead of putting the solder on the tip, put it on the wires that are being joined. Make sure there is still enough solder on the tip. Also, you may need to re-tin at some point during the process.

Melting Wires

Now, fire the wires until they can melt the weld. If your solder joint is hot enough, you should be able to see the wire strands in the solder itself. Always put the gun or soldering iron under the wires and add solder on top of the wire. 

Solder is drawn to heat, so as it melts, it pulls towards the heat through the wires, joining each strand with solder. Also, it helps to start the heat transfer by putting a dot of solder where the iron and wires meet and then moving the solder to the top. 

Additionally, putting the solder on the tip of the iron may seem like a good idea because it’s quick, but it will only make the joint cold. When hot solder reaches a cold wire and makes it hard, this is called a “cold solder joint.” It might look like the joint is good, but the molten metal is only on the outside of the wire and hasn’t been pulled through the wire strands.


Once the wire is well soldered, move the shrink tube and heat it until it fits tightly around the wire. If you want to use electrical tape instead, put it on after the solder has cooled down on its own.

Soldering VS Crimping: Which is better?

Crimping is another option available in replacement of soldering. It creates a permanent connection between two wires and a crimp terminal. It is an easy and quick method to connect two wires. Thus people think of it as a lazy way to do things. However, careless clamping of a terminal does have adverse effects on the connection.  Also, it requires proper tools. And when you are down the road, you may not have time for that. In addition, many professionals prefer soldering the wires to crimping since they seem to be the proper method of handling.

Moreover, in soldering, the connection is durable to corrosion and vibration. Nevertheless, the industry chooses to crimp over soldering. It is since the soldering is expensive and time-consuming compared to other options.

Soldering VS Crimping: Which to Choose?

You must look at a few aspects while choosing between crimping and soldering.  

Wire Fatigue

Wire fatigue is the primary problem. The wire can freely move when you connect it with crimps. Vibration-prone environments, such as adjacent to engines, benefit from copper’s elasticity. The crimp’s goal is to keep the wire in place while enabling it to move freely in the connector.

When soldering the wires, they stiffen if you are not careful. It may be due to extreme heat, although solder capillary action under the insulation causes it. If you use a small solder iron and apply heat for an extended period, it’s virtually impossible to avoid. It’s even worse for novice electricians because they tend to put too much solder at the start.


Initially, soldering may have a lesser resistance than crimping; however, this is not the case. Quite the contrary is true. When a connection is properly crimped, a colloidal steel bond is formed at the wire-to-terminal interface. As a result, the joint is effectively gas-tight, preventing oxidation from occurring inside. Since most soldiers have a higher resistance than copper, the metal connection is often superior to solder.

Crimp termination

Caption: Crimp termination

Soldered termination

Caption: Soldered termination

How Do I Properly Crimp a Connection?

As you want to try the crimping process, here’s what you will need for a good crimped connection.

Tools and Materials

  • Wires
  • Crimp Connector or Terminal
  • Wire strippers
  • Crimping Tools

Points to keep in Mind for a Good Crimp

  • You should keep the stripped wires and insulation free from damage and cuts.
  • Do not use crimping tools for Closed Barrel Terminal for crimping Open Barrel Terminal and vice versa.
  • Correctly place the wire inside the crimper for a proper connection.
  • Do not crimp since it will make the connection harder and prone to failure.
  • Protect the crimp using dielectric grease or liquid electrical tape from corrosion and moisture.
  • Also, add strain relief where possible, so that repeated bending does not affect the joining.
  • Inspect every crimp by giving it a light pull. That way, you will ensure that there aren’t any loose connections.


Remember, a short circuit of an automotive application never occurs at a convenient time. With so much riding on your car, even minor issues can be a major hindrance. But, if you’ve got the right skills in the soldering process or crimping, materials, and tools, you’ll have a solid connection and be back on the road in no time. But if your fix is insufficient to power your car and you need a complete wiring harness, you can contact us now. Here at Cloom, we offer wiring harnesses and cable assemblies to make your electrical connection with attention to detail.