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HomeTips & GuidesAuto Junction Block – How to Remove and Replace It

Auto Junction Block – How to Remove and Replace It

If you’re a car DIY enthusiast like me, you might want to know the workings of your auto junction block. 

After all, it’s the one that distributes power to various systems in your car, thus ensuring functionality, reliability, and safety. 

While this device is an able connection hub it may suffer wear and tear calls for removal and upgrade. 

Here, we see how to remove and replace an auto junction block, but before that, let’s discuss it in detail.

What Is an Auto Junction Block?

As the name suggests, automotive junction blocks are typically junctions for power distribution to various circuits and your car systems. 

You may also call it a terminal block, power distribution block, or even a wiring junction box. 

It also helps you organize your car wiring systems for seamless troubleshooting in case of an issue. 

Typically, your auto junction block will have several terminal connectors where you connect your wiring harness from different components.

 In most cases, these connectors may have color codes or labels to help you identify circuits easily. 

In addition your terminal block features relays, fuses, and circuit breakers for protection against short circuits and overloads. 

The block’s components are enclosed in a casing that protects them against dirt, moisture, and other external interferences. 

A car fuse box

A car fuse box

Types of Auto Junction Blocks

You will need to identify and understand various types of junction blocks to help you diagnose and repair your vehicle. 

We first have metallic and plastic junction boxes depending on the usage location. Although both effectively protect the box components, the metal one is more durable, while the plastic one is cost-effective and lightweight. 

In addition to classification, depending on the material, you may have differently shaped blocks, such as square and circular. 

Apart from the above classifications, let’s now dig deeper and find other types of junction boxes depending on functionality:

Main power junction block

As the name suggests, they connect to your primary power source and distribute it to major components like engines and starters. 

For instance, connecting to your car battery and then disturbing the power to your car’s main electricals.

Accessory Junction blocks

You will mainly find these in your car interior for power distribution to accessories like power windows and interior lights. 

Other examples of accessory junction blocks include integrated ECMs and BCMs for functions like climate control and security systems.

Fuse blocks

Nowadays, most vehicles have fuse boxes/blocks that protect the circuit against overloads.

 As you already know, the fuse usually blows when you exceed the current, thus disconnecting the circuit and preventing damage. 

In some vehicles, you may also get relay blocks which are electromagnetic switches to control lights, fans, and fuel pumps.

Terminal Blocks and bus bars

Your car needs terminal blocks to provide a connection point for many wires to distribute power and signal securely. 

On the other hand, bus bars refer to strips or metal bars for high current distribution to multiple circuits. 

A terminal block example

A terminal block example

How to Choose the Right Auto Junction Box

When choosing a junction box, ensure it’s compatible with your vehicle model because they are not universal. 

Secondly, you need to check its current rating to ensure it can safely handle the requirements of your car component. 

Then, see that it terminals and connectors are enough to connect your components. 

Lastly, consider its construction to ensure water, dust, and vibration resistance while enhancing its longevity. 

How to Remove and Replace Auto Junction Box

While removing and replacing your car auto junction box depends on your model, I show you the basic steps to follow:

Prepare your car and locate the junction box

First of all, you need to prepare your car by parking it on a flat surface for stability. 

From there, switch off the engine and disconnect your battery to prevent any short circuits or electrical hazards. 

Then you need to know where the box is because you cannot replace it without even knowing its location.

 In my experience, the device may be in your engine or dashboard compartment, but I recommend checking the manual.

Remove connected electricals

Now that you have parked your car safely and you know the junction box location, it’s time to remove connected devices.

 For example, remove all terminals, connectors, cables, wires, and other devices attached to your junction box. 

You must be very careful not to break any terminals or junction box connectors or damage any wires.

Remove the junction box.

As you may expect, the junction box must be tightly in place to prevent vibrations that may cause disconnections.

 For this reason, it features bolts, screws, clips, nuts, and other hardware to keep it securely in place. 

You must employ your wrench or a screwdriver to remove these fasteners and free the block. 

However, before removing it, I recommend noting the connecting wires’ position for easier and correct installation. 

If you removed it before reading this, don’t worry; you can use its wiring diagram to determine the wires’ location.

Install the new junction box.

While aligning the new box to the mounting holes, place it in position for installation. Now link the connected current supply wires as they were before. 

From there, place the mounting hardware in place and tighten properly using the necessary tools. 

Once through, reconnect the devices and wires that you removed and make sure they are in their location.

Engine compartment worker

Engine compartment worker

Connection testing

For this step, reconnect your battery appropriately, start your car, and test various devices connected to the junction box. Lastly, inspect and tighten any loose connections, and that’s it.


While auto junction boxes come installed in your car, you can use my research to upgrade yours.

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!

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