How to read a car’s fuse box

May 10th, 2023 by

Fifty years ago, your car’s electronics consisted of your radio and not much else. However, modern vehicles increasingly rely on high-tech electronic systems to operate everything from your ignition to your infotainment system and driver-assist technologies. As a result, these systems require safeguards known as fuses. These fuses act as a car circuit breaker, protecting the electrical components from damage caused by power surges.

Fortunately, fuses are inexpensive, and you can change them yourself. Your vehicle’s fuse box contains dozens of fuses, and there are numbers on the fuse box to identify which fuse controls what system. However, this often confuses car owners. To help, we asked our service experts to explain fuse boxes and how to interpret them.

Fuse Boxes Explained

A car fuse box, labeled by color and number

First, your vehicle probably has two fuse boxes. One sits under the hood, usually against the firewall that separates the cabin from the engine compartment. The fuses here protect circuits used for the engine control unit, battery, cooling systems, anti-lock braking system, and basically anything outside the cabin.

You can find the second fuse box beneath the dashboard, typically on the driver’s side. This fuse box protects cabin components, such as the infotainment tech, interior lighting, power windows, doors, and seats. If a system inside the cabin operates with electricity, it will have a fuse located here.

A Guide To Reading Fuses

A fuse box can have dozens of fuses, all with different colors and numbers. Knowing what these numbers and colors mean will help you maintain your fuses. The numbers and colors refer to the ampere rating on the fuse. Amperes represent the maximum electrical flow in the circuit. Car fuses come with 1 to 100 amp ratings in various shapes and sizes.

  • Micro2 — these fuses range from 5 to 30 amperes
  • Micro3 — 5 to 15 amperes
  • Mini and low mini — 2 to 30 amperes
  • Regular ATO/ATC — 1 to 40 amperes
  • Maxi heavy duty — 20 to 100 amperes

Fuse Color Chart

The table below details the most common car fuses by color.

Ampere Rating Color
1 Amp Black
2 Amp Gray
3 Amp Violet
4 Amp Pink
5 Amp Beige
7.5 Amp Brown
10 Amp Red
15 Amp Blue
20 Amp Yellow
25 Amp Clear
30 Amp Green
40 Amp Amber

Inside a fuse, you’ll see a thin wire filament or conductor. Engineers designed this conductor with a specific ampere capacity. The filament burns out when the electrical energy traveling through the circuit increases above its capacity. By burning out, the fuse ceases the flow of electricity, protecting the working parts of the circuit from damaging power surges.

Cars have two types of fuses. The most common fuses in cars are blade fuses. A blade fuse has two flat metal prongs connecting the filament housed in plastic. Blade fuses plug into the fuse box to complete the circuit.

A tube fuse is cylindrical with two metal ends connected in the center by glass that holds the filament. The tube inserts into two metal clips in the fuse box to complete the circuit. You find tube fuses more often in older models and blade fuses in newer cars.

How To Change a Car Fuse

Fuses don’t wear out over time like some car parts. Instead, a fuse works until it burns out, also called a blown fuse. So you can’t proactively change fuses because they don’t present wear. Once a fuse blows, the circuit it protects stops working. It could be your windshield wipers, radio, interior lights, or any system relying on electricity to power it.

So when an electrical system stops working, the first logical place to start troubleshooting is the fuse. You can find fuse charts in your owners manual indicating the position and ampere of the fuse. Some vehicles have this chart on the inside of the fuse box cover.

Before removing it, you can test the fuse using an automotive test light tool. The tool costs less than $20 and looks like a screwdriver with a fine point and a grounding lead coming off the handle. Clamp the grounding lead to metal and probe the two small test holes in the fuse with the tool’s tip. The light in the tool handle should illuminate at each port. If not, you have a blown fuse.

Use a fuse puller, a small tool that grabs the fuse, and gently remove the fuse from the fuse box. If you don’t have a fuse puller, needle nose pliers will do. Once you remove the fuse, inspect the filament within, which is the part that connects the two metal prongs of the fuse. When blown, you’ll be able to see where the filament is burned through.

Once you remove the fuse, fit another one with the same ampere rating into the slot and push to secure it. It should be level with the other fuses next to it. Some manufacturers include spare fuses in the fuse box for your convenience. If not, you can order a fuse from our parts department, and we’ll have it ready when you arrive.

Can I Use a Different Ampere Fuse?

We recommend always replacing fuses with identical ampere ratings for maximum protection. However, you can use a lower-rated fuse in a pinch to get you home or to a qualified mechanic. A lower-rated fuse may still work but will blow faster because your circuit operates at a higher ampere.

For example, if your radio has a 30-amp circuit, it has a 30-amp fuse. You can use a 25-amp fuse to run the circuit and listen to music. However, the fuse will burn out once the circuit surpasses 25 amps. It could blow immediately, or it might last a day or two.

You never want to use a fuse rated higher than the circuit. For instance, you shouldn’t put a 40-amp fuse in your 30-amp radio circuit because the fuse will allow more electricity to flow through than your radio can handle and damage your radio irreparably.

Replace your Fuse in Youngstown, OH, Today

We hope you found this blog informative. If you still have questions or need assistance diagnosing electrical problems in your vehicle, you can schedule a service visit online. One of our expert technicians can quickly test and replace your fuse and get you back to your busy life fast. Any questions or concerns you may have, trust your #1 Cochran team to get the job done.


Car’s Fuse Box by Henrique Pinto is licensed with CC BY 2.0

Posted in Tips