Fuse Box Wiring: How to Wire a Fuse Box


The fuse box is essential for every vehicle’s functioning since it aids in the smooth power flow inside the system. It protects the system from overload current or short circuits. How does it work? Let’s dig into the fuse box wiring.

Table of Contents

Understanding Car Fuse Box

A fuse panel is a circuit component that divides a power supply into several channels, each protected against overcurrent by a fuse. These panels, which are present in various electrical systems, are also known as fuse boxes or blocks, depending on the application. One prevalent form is the automobile fuse panel, which controls a car’s or truck’s electrical energy. It houses the fuses for lesser current electric accessories and electrical circuits like the stereo, power outlets, power windows, interior lights, horn, etc. 

Most electricians route high-current circuits to the power center rather than a smaller inside fuse panel. Consider the Power Center an updated fuse box. Because it is the center of the entire circuit breaker panel, it also provides a handy access point for checking resistance, circuit voltages, and continuity.

The Power Center is an advance over the older breaker box and its dispersed fuse and relay placements. Moreover, it is a beautiful spot for diagnosis because you can find most components with labels to see the relays and fuses inside.

Electric Fuse Box for Vehicle

Caption: Electric Fuse Box for Vehicle

How do fuse boxes work?

There are three essential components in a fuse box. Here is how the fuse box uses these components to smooth power flow. 


The writing’s protection is the fuse’s primary goal. Thus, you have to install and size the fuse to protect the connecting wire. For instance, if the radio draws enough electricity to melt the fuse, it will abruptly cease functioning. Moreover, replacing it is much more complex (and costly) than the fuse. Hence the fuse shields it as well as protects the wire.

When the current exceeds the allowed ampere limit, a copper wire in the fuse breaks. Each fuse has the ampere limit and multiple color codes printed on it. For safety, using the correct fuse at the right ampere is essential.


You can compare relays to electric levers because they activate other devices that require considerably larger currents when turned on. Moreover, it has an electromagnet as the essential component of the design. FYI, the electromagnet is a simple coil of wire that turns into a magnet as the current passes through it.


You will place the diodes with relays to enable direct electricity to travel in only one direction. When a system or circuit can interfere with another, the diodes frequently prevent back feeding from other lines. It will not affect the operation of your fuse box because you have to install diode/triode arrays inside the alternator.

Point Contact Diode in Car wire harness

Caption: Point Contact Diode in Car wire harness

How do You Wire a Fuse Box in Your Car?

Most cars consist of two fuse panels as a standard. The first is inside the engine chamber, with fuses for the cooling fans, an anti-locking brake pump, and the ECU. On the other side, the second fuse box holds the fuses for the electronics, controls the circuits in the passenger seat, and is on the dashboard next to the driver’s knees.

For wiring a fuse box in a car

  • Disconnect batteries from the fuse box and look for sharp edges in the service panel.
  • Since the fuse box might be near the battery, clean its loose wires first and disconnect the negative battery wire.
  • Then remove the fuse box lid and see the wiring diagram outside the cover or user guide. Now you can plug and unplug the wires according to the color coding of the chart.
  • Fix the fuse box back to its place and connect the battery as you finish the wiring replacement.
Simple fuse box circuit

Caption: Simple fuse box circuit

Source: https://rustyautos.com/ 

How Much Does it Cost to Replace a Car Fuse Box?

On average, a garage will charge you $650 to replace a fuse box with a breaker. This cost is determined by three costs: $200 for service, $365 for the new wall socket, and $90 for removing the old fuse. Moreover, replacing the defective circuit breaker in the fuse box or unit will cost up to $65. But, you can permanently save some pennies by completing the task yourself.

Problems With Your Fuse Box

You can often replace the lousy fuse or relay instead of rewiring a fuse box. Using fuse box schematics, you may determine the proper type of fuse for specific electrical equipment installed in your car. Use these to locate the fuse block, and discover the relay and fuse schemes specific to your car model. Similarly, you can choose the make and model of the car to place the particular fuse box.

Causes of Blown Fuses And Replacing a Blown Fuse

 Most fuses melt or overheat, interrupting the flow of electrical current. It can be due to

  • Age and usage,
  • Drivers overload the vehicle’s accessories,
  • As an indication of a broader issue
  • An amperage that is too high or of poor quality

Hence, it would help if you did not use a 30-amp fuse to replace a 10-amp fuse. A 30-amp allows higher electricity to pass through, while a 10-amp is meant to blow at a lower current rate.

Remove the blown fuse and fix the new one in its place. To replace the fuse, you can pull it through the socket using your fingers or a plastic puller tool. However, for bolt-in maxi fuses, you can use a screw or nut driver concerning the fuse attachment in the fuse panel.

Electrical Relay Failure and Relay Replacement

Relays with high amp loads and frequent on/off cycles fail more frequently than relays with low amp loads or infrequent use. A relay’s failure will keep the unit it controls from receiving power. Because there won’t be any fuel pressure, a failing fuel pump relay will prohibit the engine from starting. Moreover, the engine may overheat if a cooling fan relay malfunctions because it prevents the electric cooling fan from turning.

A relay that has failed has to be replaced with the appropriate component. Even if two relays have the same outward appearance, they may have different internal wiring configurations or load ratings. The incorrect replacement relay installation could lead to damage or early failure.

Never install or remove a relay in a powered circuit to avoid damaging the other electrical components. Applying some dielectric lubricant to the relay terminals is also intelligent to stop corrosion.

How to Add Wires to an Automotive Fuse Box

Typically, automotive fuse boxes have vacant fuse sockets for potential future features. Even fully equipped vehicles may contain open sockets for later-added additions by the makers. 

Moreover, you can keep extra fuses in these sockets since they do not connect to circuits. When removing spare fuses, use caution and refer to the fuse box schematic.

In empty slots of the car fuse box, you can always add accessories or power wires for tapping into the system. So, to wire the fuse box, what you can do is

  • Search for your car’s Fuse Box, either visually or using an owner’s manual.
  • Open the fuse box and find the open slot of the fuse. It is attached to the power but not to any car components.
  • Examine the Fuse tap wiring to see which connector it fits. Usually, it uses a simple slide connector but checking it before fixing it is better.
  • Strip half-inch insulation from the wire to which you will connect the fuse tap and crimp the connector to the fuse tap.
  • In the end, insert the fuse tap into the slot of the fuse box with the metal blade side first. 

How to Wire an Auxiliary Fuse Box

To wire an auxiliary box, you will follow these steps.

  • Crimp or solder a ring terminal on the fuse holder.
  • Test the fitting of a butt splice and crimp it on the inline fuse. Place a heat shrink tube on the joint.
  • Locate the auxiliary fuse box in a safe place using a waterproof bracket.
  • As the fuse box is secure, install the cable assembly by attaching the ring terminal to the fuse box and route the cable to the positive battery terminal.
  • Ensure the box is installed correctly, then pass it through a smoke test to rule out other possibilities.
auxiliary fuse box wiring diagram

Caption: auxiliary fuse box wiring diagram

Source: https://www.12voltplanet.co.uk/fuses-guide-uses.html  


Knowing the process of wiring the fuse box is handy when you want to place new components in your car. However, it would help if you also saw that your chosen features have appropriate tolerance for your needs. You can always get help from a licensed electrician and the car’s guidebooks to understand the wires correctly. Here at Cloom, we offer wiring harnesses and cable assemblies to make your connection safe and reliable.