Electrical Harness Wire: How to select one for the automotive Wiring?


Individual wires are the main component in an automotive wiring harness. However, you will need to choose a specific one to facilitate the system’s current or voltage flow. Thus, you will also need to consider many factors to selecting the wire. However, what electrical requirements are important for the wiring assembly? Let us dig into the relationship between electrical harness wire and cable assemblies.

Table of Contents

Factors to Consider when Selecting an Automotive Wire

Here, we have listed some important wire ratings. Along with it are the variables you might ignore, which is crucial.

Wire Rating

Ampacity or Current Rating

Under a defined operating environment, a wire’s rated voltage (ampacity) determines how much current is sent to a conductor and does not cause it to overheat. If you don’t know the factors that calculated the wire’s current rating, you cannot know if the wire will work in your situation.

Temperature Rating

A wire’s insulation can be used without being damaged in the temperature range. The insulation’s ability to endure an increase in conductor temperature in conjunction with an increase in ambient temperature is often measured.

Voltage Rating

When you expose a wire to a constant voltage, its insulation breaks down. It allows currents to flow into nearby electrical components or a chassis.


Ambient Temperature

Airflow at high speed may successfully manage the temperature inside an engine block. However, the increasing heat during the pitstop can be dangerous for the wire that can not handle it properly. Thus, it would help if you looked into wires that can tolerate the sudden surge in temperature.

Temp Rise

 In addition to the ambient temperature, you must keep the increased heat associated with the circuit current within the wire’s temperature rating limits.

Increased Voltage Drop

The cable size must be large enough to accommodate the needed current carrying capability and the permitted maximum voltage drop. That way, the cables won’t melt within the system, causing the system to slow down.

The number of Conductors

Most calculations are performed using a single wire in free air. A harness limits the amount of current drawn from a single wire when multiple wire assemblies are bundled together.

Terminals of Connectors

In rare cases, the cables can carry more current than the manufacturer’s recommendations on the associated connection. It is known as oversizing. Specifically, the contact rating in this instance determines the maximum electric power that a wire may carry.

Chemical Resistance

The wire complying with a test standard is subjected to a limited number of fluids over a defined period and at a specific temperature. It would help if you saw what percentage of these metrics are representative of your application.


If it is necessary to employ wire diameters lower than 20 AWG, You need to consider mechanical factors. These include vibration, flexing, and termination, among other things. As per general rule, you need to give extra support to wires less than size 20 AWG. Moreover, you should combine it with at least three more wires to ensure proper alignment in manual production.

Adjacent Material

Some wires have a temperature rating of 260 degrees Celsius. However, connectors with a plastic housing typically have a much lower temperature rating, with a maximum temperature rating of 125 degrees Celsius. These materials also affect the overall abrasion resistance. Thus it would help to consider the environmental actors while choosing the appropriate wire.

Electrical Harness Wire 1

Caption: PVC multi-cord cable

Now, Choose the Proper Wire for Your Auto

Having considered these factors, now you can decide on the wire design.

Stranded wire vs. solid wire in automotive wiring

In most automotive circuits, you will observe two types of wiring;

  • open wiring
  • and protected wiring.

However, you will use the stranded wire rather than the solid one in both cases. It minimizes fatigue breakage since it has to go through many twists and turns in the engine circuit. Moreover, experts never advise using solid wire in automotive wire harness assemblies. Yet solid wires work best in household equipment and production houses with minimal bending and abrasion chances.

Electrical Harness Wire-Gauge Wire and Wire Length in Auto Wiring

Here is a table to assist you in choosing the appropriate cable size for your electrical design application.

Electrical Harness Wire 2
Electrical Harness Wire 3

Table 1: Typical (12V) wire gauge sizes per automotive applications

Moreover, specific cable lengths can tolerate an amount of electrical surge. Hence, it would help if you considered the following table to see the gauge and length of wire to run on a specific voltage rating.

Electrical Harness Wire 4
Length of wire @ Amps  

Table 2:  Length of wire @ Amps  

Electrical Harness Wire-Wire Conductor in Automotive Wiring

Copper is mostly the best option for many device applications. However, it is expensive, so you need to look into other options, like Aluminum and copper-clad Aluminum. Most manufacturers offer two types of wires.

However, Aluminum is almost 40 percent less efficient at transferring electricity than copper is. It uses a large cross-sectional area but will get hot quickly. Also, Aluminum erodes very quickly. The natural corrosion process gets faster when you pass electricity from these wires.

 When the moisture from the air combines with the current in the air, electrolysis starts. The process makes the wire unable to conduct the current. Moreover, you might have opened a wire and seen it coated in white powder. Here, the white powder is the byproduct left after electrolysis. The same process happens for copper too, but in that case, it takes a long time, and the wire turns green.

Wire insulation in automotive electrical wiring

Electrical Harness Wire-PVC Wire

It has an extruded shielding that you will put on as it goes through a dye on the single strand. However, once this coating encounters operating heat, it melts more quickly. Hence, it is better to use PVC in places where the temperatures do not fluctuate to higher levels.

There are three types of PVC wiring;

  • TWP is lead-free, thin-wall wire with a rating of 221 degrees Fahrenheit,
  • GPT for general circuits with a rating of 176 degrees Fahrenheit
  • HDT is heavy-wall wire, with a rating of 176 degrees Fahrenheit as well.

Electrical Harness Wire-Cross-linked polyethylene Wire

Cross-linked polyethylene can withstand more heat. Moreover, created by heating and pressuring the material by a tube, “cross-linking” the molecules makes the wire more durable under high temperatures. Thus, it is suitable for use in cars.

In Cross-linked wires, you can get there four variations:

  • TXL with the thinnest layer of insulation
  • GXL has a slightly thicker layer than TXL
  • SXL features a thicker insulation layer than GXL
  • SGX with the thickest insulation layer among all the cross-linked wire families.
Bare copper-stranded wire

Caption: Bare copper-stranded wire


Choosing wires is hectic, but you have to ensure reliability, safety, and prevention of failure. Although there are a lot of ratings and variables that can influence a choice, the size and material are the first things to consider. Here at Cloom, we offer wiring harnesses and cable assemblies, so your connection is made with attention to detail.