DIY Wire Harness: Step-by-Step Guide To Build A Wire Harness

Wire harness assemblies are an integral part of all-electric systems, and all-electric systems come with factory-made harnesses. However, sometimes, you need to build your harness to improve its appearance or make it fit for an application. If you know the basics of wire harness making, it becomes easier and less time-consuming. This blog post will teach us how to construct a DIY wire harness assembly.

Components that make up a Custom Wire Harness

Wire harness assembly comprises wires, cables, terminations, connectors, sleeves, and other things that help organize these parts in an extensive electrical system. 

Wiring harness wires

Wires are the main component of wiring harnesses. There is either a single conducting strand of aluminum or copper or can be braided or stranded wires. The use of different wires depends on the needs of the project. 

Sometimes, you may also need different gauge wires in the same wire assembly to provide multiple functions. According to the AWG system, manufacturers use standard gauges in wire harnesses 10, 12, and 14.

In addition, standard wire colors and their functionality are:

Black wires: indicates a hot/positive current

White wires: indicates a negative current

Green wires: mainly used for ground wiring in residential applications

Red wires: work as a secondary line for hot/positive currents

Blue wires: designates a point of connection


The electrical industry uses different standard cables. These cables typically have a neutral, hot, and ground wire. Each of these wires twists and bonds together to form a single wire. The cable wires have PVC insulation or others to prevent shocks. Also, the color coding of insulation helps identify the wires.

Different cable standards help engineers design a system based on cable specifications. As a result, they save a lot of time and money rather than manufacturing the harness from scratch. UL-certified cable types include TPT, SPT-2, SVO, TST, SJE, and SJOOQ. 


There are connectors available in different shapes and sizes, but there are specific connectors for a particular cable. For example, in a complex custom wiring harness, you can find socket-type connectors, dip connectors, d-sub connectors, and card edge connectors, along with ribbon cable connectors.


When you terminate a cable at the connection point of equipment, wall outlet, panel, or any other device, you need to terminate it perfectly and safely. You can find endless terminations options, including insulated or non-insulated spades, ring terminals, hook terminals, and others.

The tools & parts you need for building a wiring harness

While building a wire harness, you need to make several electrical connections for which you need to do splicing and termination. As a result, you may require some tools to get the job done. 

Electrical tapes and cable ties 

These will help shield the wires and cables from abrasion, essential for preventing electrical fires.

Soldering iron

You can use it for splicing wires. Though the process is time-consuming and requires skill, it’s much more professional and robust. You may also need heat shrink tubing to complete the process.

Wire cutters and crimpers

Other than soldering iron for splicing wires, you may also need to make a crimp connection. Thus, you may also need a wire cutter and crimper. You can also take an automatic wire stripper.

A helping hand station

You may also need a helping hand station where a clamp holds the wires together while working.

A dielectric grease

You may also want a dielectric grease for installing the wire harness.

A workbench

You will need a workbench with vast space to extend the harness.

automotive industry manufacturing wiring harnesses

Caption: automotive industry manufacturing wiring harnesses

Build an automotive wiring harness at home

Running the wiring harness through the vehicle is the most daunting task. There are chances of cuts and bruises while hooking wires and different dash components. So, it’s better to be safe. Always wear your safety glasses and gloves while working. Further, there are high chances of electrical shocks and fire. So, always keep a fire extinguisher with you. Also, ensure that you do not supply any power to the harness while working; otherwise, it can be hazardous. Also, take precautions while moving parts with sharp or dull edges, as it can damage the casing.

Study a schematic

While building wire harnesses, you will have to refer to the schematics or wiring diagrams. With the right schematics, you can be sure that you are making the right connections. Also, it helps you to avoid tapping harmful wires in power devices. The cable harness diagram also saves time if you study them before building.

Lay out your harness

If you are replacing an old harness, it can work as a reference point for building a new one. So, lay it out and try to understand wire lengths and routing.

Decide where to mount the fuse block.

Mainly, it will not mount at the old location, thus throwing off the measurements for some wires.

Take note of routing in the car.

You need to learn where to run the wires before making connections. When you know this, you can cut and splice the wires without any potential mistakes. It is the most annoying job in the whole wire harness-building process, whether a short harness or a long one. You can take the help of the factory wiring diagrams. Some universal-style harnesses come with proper labeling to make things easier.

Replicate your wire routing on the workstation

Create a replica of the wiring diagrams in the car on your workstation. With this, you need not run back to your vehicle a hundred times, and also, you will get much more accurate results. Simply trace the dimensions and lay the wire on them.

Separate, Protect, and Secure

Separate all the wires before splicing. Add wire tapes, looms, or sleeves to prevent the tangling of the wires. Once done, take the harness to the car for the last mockup.

Source old connectors 

Now, you can cut connectors from your old harness and put them in the new one. However, start one by one; otherwise, it will confuse you. Take notes in a notebook, or draw pictures or label wires to clarify things. 

Instead, you can also use crimp connectors, but the finish could be better.

Strip the wire

Take a wire stripper and remove a small portion of the wire insulation from one end. Remember, you must attach wires to terminals and cut them according to the terminal size.

Cut the heat shrink

Cut a heat-shrink tubing longer than the stripped wire length, and insert this tubing over the unstripped part of the wire.

Attach a terminal

  1. Pick a terminal, put its seam into the pliers, and crimp it slightly.
  2. Insert this terminal onto the wire and squeeze the wire and terminal with the pliers.
  3. Apply enough force to crimp the wire and not damage them.

Cover the wire

Next, pull the shrink tubing over the crimped edge of the wire and the terminal. Make sure that the tubing closes the two parts completely and tightly.

Shrink the tubing

In this step, you need a heat gun. Switch on the gun set the required temperature, and let it warm. Now direct the hot air from the gun over the heat shrink tubing.

worker packing wiring harnesses

Caption: worker packing wiring harnesses


Hope you learn how to build your wiring harness. If you have any issues, you can ask for custom design wiring harnesses from Cloom. We are a leading manufacturer of custom cable assemblies, and wiring harnesses suitable for various applications.

Hey, I am John, General manager of Cloom and OurPCB.

I am a responsible, intelligent and experienced business professional with an extensive background in the electronics industry.

Reach me at [email protected] to get a quote for your projects.


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