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Wiring Harness Standards for Automotive: Why is it so important?

About Wiring Harness Standards for Automotive, automotive industries have used standards to manufacture reliable vehicles for a while. 

These standards oversee the wiring of cars allowing manufacturers to produce reliable vehicles. 

Please understand these standards correctly to avoid some troubles in production.

This article will discuss the wiring harness standards for automotive and why they are important in the auto industry.  

Let’s begin!

Table of Contents

What is a Wiring Harness? Definition

A wiring harness acts as the main body of the network circuit in a car. It comprises wires, connectors, and wrapping tape. 

an automotive wiring harness

(an automotive wiring harness)

Why are auto industry standards important?

Usually, standards are in place to promote familiarity and reliability. It is also the case in the auto industry.

They ensure that vehicles and vehicle components are reliable. Also, these standards help to ensure product quality, its impact on the environment, and the ethics around labor and sourcing. 

Every manufacturer has to follow all the implemented standards to the latter. Failure to which may result in huge fines and unreliable products.

For instance, auto industries use many electrical components which are susceptible to cause electrocution, overheating, and fires.

Therefore, these engineering standards work to reduce such effects, enhancing product quality.

Standards are also very important because they ensure every manufacturer meets the technology demand in the market.

It is because technology is rapidly advancing, and there’s a need to build cars that fully utilize this technology.

Lastly, there are engineering standards that prevent every auto industry from manufacturing its parts and spare parts. These licenses have been given only to specific vendors. It is important to ensure uniformity and compatibility of the product. 

electric wiring

(electric wiring)

Knowledge of SAE, UL, and ISO standards

There are only three organizations worldwide that set all the engineering standards. These include

  • The Society of Automotive Engineers (SAE)

is the most predominant organization in setting automotive standards. It has existed for more than a century and thus has vast experience in handling automotive practices.

Its main focus is ensuring manufacturers produce properly rated and functioning products.

Some of their standards and what they cover: 

  • SAE J1127- battery cable specifications.
  • SAE J1127- ships’ ignition protection.
  • SAE J1171 – primary cables having low voltages.
a car wiring system

(a car wiring system)

  • Underwriters Laboratories(UL)

Underwriters Laboratories(UL) was previously called Underwriters’ Electrical Bureau.

The UL standards focus on the certifications and safety of electrical components and materials against fires and fire insurance policies. 

Some popular UL automotive wiring standards include 

  • UL 83 Thermoplastic cable
  • UL 44 Insulated Rubber wires
a product testing method

(a product testing method)

  • International Organisation for Standardization (ISO )

ISO has its headquarters in Switzerland. It’s an organization consisting of 167 countries, each with standardization practices. 

The main focus of ISO is anything outside the electronic engineering process. They set standards on issues involving product quality and its effect on the environment.

The following are some of the standards in place in the International Organization for Standardization:

  • ISO 8846 covers all small electrical components
  • ISO 9001 is a suitable quality business standard for companies and organizations.
  • Other industry standards

There are standards that either SAE, UL, or ISO do not cover. For instance, companies like CHRYSLER and FORD have heat resistance specifications and standards that are above SAE standards.

Also, RV INDUSTRY has different standards specific to recreational vehicles.

Wiring Harness Standards for Automotive:  product quality testing

(product quality testing)

Automotive Wire Specifications

Car wires come in different sizes for different functions. 

0.5mm2 gauge wire connects to the door, indicators, dome, and instrument lights. 

0.75mm2 functionalizes the brake lights, rare and front lights, and license plate lights. 

1.0mm2 wire is mainly for fog lights and turn signals, 

1.5mm2 is for headlights and horns.

The wire to the main power should be larger, usually between 2.5mm2 and 4mm2.

You must know your car’s needs to determine the specific wire size. Specifically how much load the current carries. 

Wiring Harness Standards for Automotive:  a car wiring system

(a car wiring system)

Types of Vehicle Harnesses

A car’s wiring harness has 3 main subdivisions. The front wiring harness, the rear wiring harness, and the wiring harness on the roof. Each of these divisions holds specific car features.

The front wiring harness holds sections like the engine, instrumentation, air conditioning, front light assembly, and batteries.

Similarly, the rear wing harness holds the tail light assembly, luggage compartment, and license plate light.

Lastly, the harness on the roof is responsible for the audio speaker, door, and roof lights. 

  • Standard car wiring harness

The name of a wiring harness circuit comes from the number of features it can offer. The most basic circuit is a 12-circuit.

This circuit holds only 12 basic features of a car. However, if you need advanced features, you will need an 18-circuit or a 24-circuit. 

The table below shows accessories in each circuit:

12 circuit18 circuit24 circuit
RadioTurn signalsGaugesWipersHornStop lightsTail lightsHazard flasherHeat and A/CDash light sparking lightsDistributorAll accessories are in a 12-circuit. Electric fuel pump power windowsElectric fanRadio B+ memory high mount brake light power locksAll accessories in an 18 circuitClockDome lightUnderhood lightTrunk light lighter
Wiring Harness Standards for Automotive:  different wiring harnesses.

(different wiring harnesses.)


All manufacturers need to mark the end of every connection using symbols or numbers. This is necessary so that it makes it easy to identify by the operator during repair and replacements. 

Wiring Harness Standards for Automotive:  The electrician operated the wires according to the drawings

(The electrician operated the wires according to the drawings)

Winding method of the automotive wiring harness.

Wrapping a harness protects it from external damage. There are different ways to wrap a wire harness. All this depends on the location of the harness.

For example: 

  • Since an engine harness operates in harsh environments, the wrapping pipe should be waterproof and flame resistant.
  • For an instrument line, you will wrap it with a flower or full wrap. This is because the line is in a small working space, and the environment around it is good.
Wiring Harness Standards for Automotive:  Wires that haven't been wrapped yet

(Wires that haven’t been wrapped yet)


Every licensed manufacturer must rely on the standard to produce quality products. It is illegal for your products to be in the market if they do not meet the necessary automotive standards.

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