Building a Wire Harness: An ultimate guide on DIY Wire Harness Assembly

In every industry, electricity is important to keep up the good work. For that, you need to use an electric wire harness. Now, you can get it ready-made in the store, but it might not be able to fulfill your intended use. In that scenarios, you might want to customize the wire harnesses for your task. Also, you may want to improve its appearance by adding tags and colors. Either way, we suggest a cost-effective and better way; building a wire harness yourself.

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Components Making up a Wire Harness

It would help if you had various components to build a wire harness.


Individual wires are the most basic components. And when choosing the single wire, you should consider the following.

Wire size

According to the American wire gauge, the bigger the gauge number, the smaller the diameter of the wire. Hence, you will determine the wire gauge by two factors: the accessory’s required current and the distance the wire must travel to reach the power source. You will need a bigger gauge wire to power an accessory with a higher current draw effectively.

Wire material and construction

Aluminum or copper is common for conducting current in wires. Stranded copper wire is a top pick for automotive applications due to its malleability and electrical conductivity. And  Solid one is ideal for outdoor use where more durability and higher currents are required.

Wire color

It’s simple to overlook the significance of wire color unless you’re trying to track down a defective circuit. In the wire harness manufacturing process, you can easily track each cable that goes where if you label it.

Standard colors and functionality include:

  • Black wires typically designate a hot or positive current.
  • White wires will typically be for negative currents.
  • Green wires are typically for ground wires, especially in residential wiring applications.
  • Red wires can be a secondary line for hot and positive currents.
  • Blue wires are good for designating a point of connection. 

The ideal part of cable and wire colors is the vast degree of customization.

Wire insulation

Wire insulation plays a key role in safeguarding the wires within a wire harness assembly, yet it often goes unnoticed. When constructing a wire harness, a cable engineer must consider the system’s expected exposure to moisture, temperature extremes, acidic compounds, and other external conditions.

Insulation materials typically used in wire harness assemblies are:

  • Polyvinylchloride (PVC) is a cheap but durable material used for low- to medium-voltage cables.
  • Polyurethane (PU) is typical insulation to shield wires from moisture and abrasion; it can be either thermoplastic or thermosetting.
  • Thermoplastic elastomer (TPE) is a versatile material since it is both elastic and resistant to cracking under stress.
  • Thermoplastic vulcanizate (TPV) is a subset of thermoplastic elastomers (TPEs) that vulcanizes at elevated temperatures, lending it a superior compression set and thermal stability.
  • Polytetrafluoroethylene, or PTFE, is a strong chemical that is an inert form of epoxy resins. Mostly, electric systems use it because of its versatility and great performance in extreme temperatures and wet environments.
  • Silicon insulation provides better heat resistance because of its wide thermal range. When dealing with wide temperature changes, silicone is the best insulation material.
Components of wiring harness

Caption: Components of wiring harness

Connectors and terminations

To properly insert a cable into the connecting point of a panel, equipment, wall outlet, or another device, you must select the right connector with the proper terminal. There is an almost infinite variety of terminations that you can use in your desired field.

Soldered and solderless (crimp connectors) are the two most common forms. Oversized wiring or splicing calls for the use of soldered connectors. All additional wiring can be crimp connectors, which is what we advocate utilizing wherever possible.

You can rely on a solid connection from a solderless connector; they’re a breeze. The insulators of most solderless connections have color codes to indicate the wire gauge to show the specific functioning. There is a wide range of solderless connector types available, including:

Butt Connectors

Cylindrical butt connectors connect two separate wire ends. You will place both ends of the wire into the connector and crimp them down.

Spade Connectors

For frequently repaired or replaced parts, spade connectors are the way to go. Here, you will make a connection when a male connector on one end of the wire inserts into a corresponding female connector on the other. However, you can always pull the plugs in opposite directions to detach them.

Ring Connectors

Ring connectors are essential to prevent the wire from slipping out of screw-type terminals.

 Wire harness connectors

Caption: Wire harness connectors


Sleeves have several advantages, including protection from the sun and abrasion, better cable management, and more. It’s common practice to utilize a variety of sleeves in wire harnesses, some of which are:

  • It’s customary to use Velcro sleeves because they’re simple to fasten.
  • Spiral polypropylene wraps are available in a wide range of diameters. Incorporating UV protection in addition to enhanced durability. Superb for controlling your color palette.
  • Braided sleeves are not only aesthetically pleasing but can also be heat shrunk to fit a particular set of cables and connectors.
  • Polyethylene spiral wrap provides adequate protection for wires against heat and normal wear and tear at a low cost.
  • Shrink tubing is useful for protecting connections when soldering or using solderless methods. In addition to protecting against electrical shorts and the elements, shrink tubing can be quickly and easily installed.
Wire harness connector with terminals

Caption: Wire harness connector with terminals

Overload protection

Overload protection is essential for safeguarding expensive electrical equipment. The following are the primary methods of overload protection.


The fuse blows when the circuit gets more current than the fuse threshold. The most common fuses are 3, 4, 5, 6, 7.5, 10, 12,5, 15, 20, 25, and 30 amps, with other sizes also available. Hence, its best practice to use a fuse with a slightly greater rating than the accessories. For safety, use a 25 amp fuse for an electric fan with a 19.5 amp rating.

Fusible links

You can also use fusible linkages. These are not typical copper wires; they are alloyed with a lower melting point. The connection is made directly to the accessory’s power cord. The link will melt in the instance of an electrical overload.

Circuit breakers

If an overload occurs, a breaker will cut power to the appliance. Once the cause of the overload is eliminated, you can reset the breaker. Circuit breakers are available in manual and automatic reset varieties in the same widely used amperage ratings as fuses.


When wiring, if your electric devices have higher current consumption than a regular power switch can handle, you should also install relays. Most switches can only handle low currents. Therefore wiring in an aftermarket electrical accessory almost always necessitates a relay. Large electric fans, fuel tanks, and high-intensity discharge (HID) headlights are just a few examples of high-amperage electrical accessories that benefit greatly from the employment of relays. An electric coil switches them on and off. A closed relay prevents electricity from reaching the disconnected device. When an electrical accessory is activated, power is transmitted via an electric coil through a relay.

Rubber damaged surface due to overheating

Caption: Rubber damaged surface due to overheating

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Mapping the strategy before starting DIY Wire harness manufacturing projects

Make sure you have a plan before you start wiring anything. Make sure you have enough wire to finish the job by laying out the wiring or wiring harness. Also, you should install the required fusible links, relays, or breakers at the power supply and electrical device connections.

Each cable and harness should be clearly labeled with the components they connect to if they aren’t already. Grommet the hole in the firewall where the wiring or harnesses will pass to prevent the wires from severed by the metal. When the wires have passed through the wall, only then should you tighten the connectors.

Here, you need to locate the negative-side chassis ground at one position. Moreover, your common grounding point for the harness should be near the firewall. This strategy can easily reach the vehicle’s negative side with ease. Additionally, when connecting the common ground to the chassis, use a 10 gauge or larger wire. Take your time, keep everything neat, and you’ll soon be a wiring pro!

Designing and Testing cable harness

Caption: Designing and Testing cable harness

Steps to Build a Wire Harness

The fundamental criteria and procedures for creating a wire harness are as below.

Construct a Wiring Diagram

It would help if you first created a wiring diagram for your system before you can start cutting any wires. Utilizing a computer program like CAD will allow you to complete this. A wiring diagram typically consists of two components: a schematic and a harness. The pieces, their locations, and their connections will all be shown on the schematic.

You can use the harness diagram to make a precise plan for connecting each component. And color the diagram to represent the many components. Circles of various colors, for instance, can represent connectors.

Gather Your Resources

You’ll need these proper tools:

  • Wires
  • Snap ties
  • Heating gun
  • Connectors
  • Terminals
  • Multimeter
  • Wire Cutters
  • Crimping Pliers
  • Heat-shrinkable tube
  • Wire Strippers (manual or automatic)

The size of the terminals will determine the diameter of the heat-shrinking tubing used. For that, choosing GXL cable with PVC is wise because wire harnesses are frequently used for demanding applications. This wire can withstand high temperatures, making it perfect for severe settings. Moreover, it will provide heat, flame, moisture, and chemical resistance to the wire.

Strip the Wire

Take a tiny section of the insulation off one end of the wire using the wire stripper. You must ensure that the cut length corresponds to the size of the terminals. It is because you will attach the wires using terminals.

Building a Wire Harness: Cut the Heat-Shrink Tube

Heat shrink tubing should be cut so that it is slightly longer than the length of the bare wire. Over a wire segment that hasn’t been stripped, place the heat shrink.

Building a Wire Harness: Connect the Terminal

Take a terminal, insert its joint into the crimping pliers, and slightly press it to attach it. Using the pliers, squeeze the terminal and wires together after inserting the terminal into the wire. Use enough pressure to crimp the two pieces together without damaging the wire.

Building a Wire Harness: Cover the Connection

After finishing the previous step, place the heat shrink tube over the crimp edge and seam to cover the wire. Make sure the tube fits the two sections securely.

Shrink the Tube

Use a heat gun to shrink the tube at this point. Activate the gun, adjust the temperature, and give it a moment to warm up. Heat shrink tubing by directing the hot air from the gun over it.

Caption: Cable harness in a car

Caption: Cable harness in a car

The Safety Brief When Building a Wire Harness

Automotive wiring is the surest way to get a few scrapes and bruises on your knuckles. Cuts are inevitable whenever you work with sharp objects, even if you’re merely installing a new radio. Moreover, dust and dirt can get into your eyes if you’re dangling behind the dashboard. Even though wearing safety goggles and gloves can sometimes be painful, they are essential in this work area. So, you need to wear them at all times.

In addition, electrical shocks are quite dangerous. Accidents happen, and if you’re not careful, they might lead to a fire, so stock up on fire extinguishers. Due to the possibility of electric shock, you should never connect the wiring harness to electricity while working on it. Also, keep in mind the location of the wire as you work. Avoid all moving parts, including those with smooth or rounded edges. The constant rubbing will eventually wear away the protective coating, leaving you in a precarious situation.


Building your wire harness, you need to be careful while making the strategy and choosing your tools. But if you need more professional cable assemblies and wiring harness solutions, contact us now.

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