Five-Star Manufacturer
Fast Delivery
Customized Service
HomeTips & GuidesEngine Wiring Harness: Its Functions and More!

Engine Wiring Harness: Its Functions and More!

About Engine Wiring Harnesses, Most individuals see or utilize autos daily.

These automobiles have electrical systems that contribute to their optimal operation.

As a novice mechanic, understanding how an engine wiring harness operates can be a concern. 

We can learn more about engine wiring harnesses through this article, so let’s get started!

Table of Contents

Definition of an Engine Wiring Harness

An EWH harness comprises terminals, wires, and connectors that run throughout the machine.

The harness transmits power and controls information to vehicle components like batteries and audio systems. It is an important piece to the overall reliability of a car.

(Engine Wiring Harness)

What are the Key Functions of an Engine Wire Harness?

The key functions of an engine wiring harness include the following:

  • It is the Heart of the System

Without batteries, your system is as good as dead since power from the batteries gives life to the whole system.  For instance, a section of an engine harness supplies power to the fuse box from the batteries. 

  • It Acts as a Fuse Box

A fuse box connects to the engine via a wire harness. A fuse box in a car works to prevent electrical fires by stopping very strong currents.

It controls the amount of power traveling to the engine, headlights, and other components.

  • It Helps You Understand Your Electrical System

You have to have the necessary knowledge before working on an electrical system. A diagram of an engine harness can help you understand the whole system. 

  • It Helps You Avoid Making Mistakes

It is important to look at photos of a harness when studying the system. Analyzing the photo will help you know how the cables run and where they connect.

It will prevent you from making mistakes when repairing or installing.

an engine ecu control unit.

(an engine ecu control unit.)

Common types of EWH

Types of engine wiring harnesses include:

  • Airbag Harness: Determines when an airbag will open.
  • Main Harness: This harness guides the car’s control panel and electronic systems.  
  • Engine Harness: An engine harness handles some major engine functions. Such functions include; air pipes and pressure.
  •  Body or Floor Harness: A body wiring harness, also called a floor harness, ensures the speakers, air conditioning, and navigation systems are working.
  • Battery Harness: This harness connects the engine with other car parts. It works by relaying power to these components. 
  • Door Harness: As the name suggests, this is a car door feature. It controls every feature on the door, including window and door lock features.
  •  Roof Harness: A roof harness is a feature on the car’s roof that directs parts like the sunroof. 
  • Front Harness: This harness controls the power, speed limit, and oxygen sensors. 
an automotive wiring harness

(an automotive wiring harness.)

Symptoms of a bad engine wiring harness

  • Broken wiring harness:

For this problem, you’ll notice the speedometer of a moving car will be at zero, and the odometer will register a smaller mileage.

Cause: short branch design, twisting the harness during assembly, and a non-standard manufacturing process. 

  • Harness wear

When you have harness wear, sensors will start to malfunction.

Cause: poor assembly and layout and a lengthy branch design. 

  • The wiring harness assembly plug is broken.

The problem will manifest in the fault light for a damaged plug since it will always be on. 

Cause: Poor product quality and assembly process.

  • The wiring harness assembly plug contact is poor

This problem occurs when the engine fails to start.

Cause: Poor assembly process, wrong plate setting, manufacturing problems.

a car wiring system

(a car wiring system.)

How to Diagnosing a Broken Engine?

Identify the faulty fuse box.

Identify the fuse causing the component to malfunction. If several components are malfunctioning, identify the common wiring points to these components.

It will direct you to the areas that need inspection and testing. 

Inspect and Test the Fuse

If the fuse is faulty, immediately replace it with a functioning one with a similar rating.

Inspect and Test Other Component and Wires

After finding all the faulty components, mark all the wires coming from them. Do this carefully, especially with older engines. Replace all worn-out wires before continuing with the diagnosis.

a mechanic diagnosing a car engine

(a mechanic diagnosing a car engine.)

Conduct a Voltage Drop Test

To do this test, you need a multimeter. This test is necessary for finding openings in the circuit. 

For example, the switch might be faulty if you connect the multimeter and the electricity is not flowing. 

Examine the Wiring Harness

It is the next step if all the other areas function correctly. Firstly, you will need to disconnect all the wires and test them. An ideal wire registers a resistance of 0.3-0.5Ω.

Otherwise, replace the affected harness section or the entire wire if you find a faulty wire.   

Use a multimeter to detect car wiring harnesses

(Use a multimeter to detect car wiring harnesses)

How much does it cost to repair an engine harness?

The repair cost may vary depending on the damage amount and which part needs repair. Some repairs need professionals so that labor costs can add to the total repair cost. 

However, always keep in mind that safety should always come first. Spending lots of money is necessary. It is if you want to reduce the likelihood of accidents and fires due to poor repairs.

a mechanic repairing a car.

(a mechanic repairing a car.)

How to Avoid Wiring Harness Problems?

Incorrect Wire Preparation and Staging

Under this step, you first have to choose the correct wire. Next, you have to cut the wire to the desired length. Lastly, ensure you strip the ends. 

Poor Wire Harness Layout

Working on a board to prevent yourself from wrongly laying out the circuit would be best. Working from a board will let you know how many wires are missing and the place where each one goes.

a motorcycle wiring

(a motorcycle wiring)

Shoddy Labeling

Poor labeling is a problem that affects a majority of manufacturers. Hence the introduction of software that checks for label accuracy before printing. 

Defects in the Crimping Process

It is important to crimp wires carefully. Failure to which might result in open circuits. 

Defects in Soldering

Some of the soldering effects include an incorrect soldering temperature and poor soldering techniques. These issues will always affect the finished product.

Wrong or Missing Hardware

It is easy to overlook some mistakes when hurrying to meet a deadline.

As a technician, you should always double-check every connection and ensure they follow the regulations. 

hardware parts of a modern car.

(hardware parts of a modern car.)

How to replace an Engine Wiring Harness?

You do not necessarily need to be an expert for this procedure. All you have to do is follow the following steps:

Take pictures of the circuit.

Take enough photos from all angles of the entire circuit. Then get a manual and study the wiring diagram of an engine. Carefully observe the colors of the wires and how they run since these colors fade with time. 

Disconnect the car battery.

Remove all the clamps in the terminals using an appropriate wrench. Start from the negative terminal and finish with the positive. 

Carefully disassemble the Current Harness.

First, you have to remove the bulkhead.

Secondly, unbolt anything holding the harness in place.

Next, unplug the alternator and starter. Lastly, ensure you remove all the hidden sensors.

Slightly raise the vehicle.

Jack up the vehicle so you can remove all the connections underneath the car.

Some harnesses usually intertwine with an engine harness.

Therefore, locating and isolating them is important since you do not have to disconnect them entirely.

Mark the new connections

Label any new connection using masking tape. It helps with planning and organization.

Also, untangle any wire and go through their routing and installation process. After, connect the new wires. 

Position the New Wiring

Install all the necessary new wires and secure them within the engine chassis

Any loose wire should be kept from moving parts and the exhaust pipe. You should remove the jack, place the battery, turn on the engine, and check for functionality. 

Automotive wiring harness

(Automotive wiring harness)


Before repairing a car, make sure you know the car wiring system.

Additionally, always use products that guarantee quality and longevity. It will help you save on time and money spent on repairs.

We hope our guide enlightened you on every question about an engine wiring harness. 

I am Lillian Yang, having been a sales manager for over 10 years.

I have received many positive reviews from customers. They have praised our excellent service, on-time delivery, and high-quality cable assemblies.

For your projects, please provide cable assembly files/images/smples, etc., so that I can send you a quotation within 24 hours.

Contact me now and let’s get started on building your wire harnesses!

Background media

For Better Future
and Business
Let’s Talk Now!

Fill in your details and we’ll get back to you in 24 Hours.

Contact Form Demo


[email protected]




3rd Floor, Nanhai Plaza, NO.505 Xinhua Road Xinhua District,
Shijiazhuang, Hebei, China. 050057


© 2007- 2023 Cloom tech. ALL RIGHTS RESERVED.



Subscribe to our newsletter for the latest updates, exclusive offers, and exciting news delivered straight to your inbox.