One of the major culprits of an electrical surge in most cars is a blown fuse. Located in your car’s fuse box, a fuse comprises a thin wire strip that melts whenever a strong current passes through. The main purpose of this is to protect your fragile components from getting damaged by excess electrical current. So, learning how to tell if a car fuse is blown is usually the first step of troubleshooting this common problem.
Most modern cars are designed with multiple fuses that protect various electrical components. Each fuse is located in its own circuit. Since some components demand more power than others to function, fuses with different amp ratings are hence needed to protect such components.
So, in case you notice that some of your car’s electrical components are failing, then there’s a high possibility you’re suffering from a blown fuse. With that said, this short guide will explain why car fuses blow, list some common signs of a blown fuse and lastly, discuss how to tell when a fuse is blown and how to replace it.
Understanding Your Car’s Electrical System
Your car consists of three electrical systems that are the battery, the starter, and the alternator. The battery provides the electrical current, which is supplied, to the starter. The starter is then responsible for starting the engine.
Once the engine starts, the alternator takes over by keeping the battery fully charged. Additionally, the alternator is responsible for converting the battery’s DC into AC to power most of your car’s electrical components.
The current generated by the alternator is mostly used to power different circuits within the car. To protect these circuits from damage caused by a power surge, fuses are used and are mostly located within the fuse box.
Fuse boxes can range from two to four depending on the type of car you’re driving. In most cases, fuse boxes are located in the car’s trunk, under the hood, under the rear seat, and beneath the dashboard. However, it’s highly recommended that you consult your car’s manual for the exact location of the fuse boxes.
Why Do Fuses Blow?
Now, in case you’ve experienced a blown fuse at one point in life, then you must be wondering what exactly causes these fuses to blow. In this section, we’re going to discuss three common reasons that cause fuses to blow.
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Short Circuit:
One of the common causes of blown fuses is a poor connection between two conductors resulting in a short circuit. When a short circuit occurs, your car’s electrical circuit detects an electrical overload. To avoid damaging your car’s electrical components, the fuses connected to that circuit automatically blow.
In most cases, a short circuit is caused by any of these three factors.
- The first one is an exposed wire that gets into contact with your car’s chassis.
- Another factor is a malfunctioning electrical component such as the windshield wipers or the power windows. In case these components demand a higher current flow, then they’re likely to cause a circuit overload that can result in a short.
- Lastly, when a conductor is exposed to the elements, such as water leaking into the car’s chassis, then this flaw is likely to short your car’s circuit.
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Incorrect Amperage Rating:
This is when a blown fuse is replaced with one of higher amperage. You see, car fuses come with different amperage to suit specific power demands. When replacing blown fuses, always ensure that you confirm with your car’s manual for the correct amperage rating.
Signs of a Blown Fuse
If you’re an experienced motorist, then it’s quite easy to tell when your automotive fuses are blown. Since fuses are just simple components that prevent power overload, they mostly cause minor electrical issues when they blow. So, which are those signs that point out to a blown fuse?
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Loss of Power:
One of the common symptoms of a blown fuse is the loss of power to one or more of your car’s electrical components. This might be the radio, the car’s air conditioning system, the internal lighting, the windshield wipers, or the power windows conversion kit.
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Blown Fuse:
Another more direct sign of a bad fuse is a blown fuse upon retrieval. Now, if you happen to locate the fuse box and you discover that some of the fuses are cloudy and appear burnt, then that’s a direct sign that you’re dealing with a blown fuse.
How Do You Tell That a Car Fuse is Blown?
Gather Your Supplies:
- Flashlight
- Digital multimeter
- Fuse puller/needle-nose pliers
- Step One: Locate the Fuse Box
Now that you’re certain your car has a damaged or faulty fuse, the first step of troubleshooting this electrical problem is to locate the fuse box. Since the fuse box is the one housing the fuses, finding it will help you locate and replace the faulty fuse easily.
But, locating the fuse box is not as easy as it sounds. That’s because the location and the number of fuse boxes in your car will differ greatly depending on your car’s make. You see, some cars have two fuse boxes while others have up to four.
Also, the location of the fuse boxes can differ greatly from under the hood, in the trunk, under the dashboard, or under the rear seat. But, since most cars have an owner’s manual, it’s always advisable that you refer to the circuit diagrams to determine exactly where the fuses are located.
- Step Two: Locate the Exact Fuse
Once you’ve located the fuse box, the next step is to locate the exact fuse that’s assigned to control the device that has stopped working. To do that, you’ll have to open the fuse box lid to view the diagram that indicates the specific components that correspond with each fuse. You can also refer to the owner’s manual for this diagram.
Besides, the diagram will give you any information regarding the size and the amperage rating of each fuse in the various circuits. Such information is considered vital, as it will help you massively when buying a replacement.
- Step Three: Pull off the Fuse for Inspection
With the car turned off, hold the fuse in question with your fingers and pull it off. In case it’s too stubborn to get off, use a pair of needle-nose pliers, fuse puller, or tweezers to pull it off. With the fuse out of the fuse box, inspect it visually for any signs of damage.
Here, you can inspect the filament metal inside the clear plastic housing to see whether it’s intact or broken. In case the thin metal inside is broken, then it means the fuse is blown. However, if the metal filament is intact, then it means the fuse is in good condition.
- Step Four: Testing the Fuse
In case you’ve inspected the fuse and you’ve seen no signs of damage, then the next step is to employ any of these two methods to guarantee the fuse isn’t damaged. The first step is to use an automotive test light to test the fuse.
To perform this test, you’ll need to turn your ignition key to accessory mode also known as Key On Engine Off mode. Next, attach the grounding lead of the test light to the car’s metal chassis. Probe the tiny test ports of the test light on the face of every fuse.
If the test light illuminates, then it means the fuse is not faulty. However, if the test light doesn’t illuminate, then it simply means the fuse in question is blown.
The second method you can employ to test a blown fuse is by using a digital multimeter. To do this, you need to turn the ignition key to accessory mode. This will allow electrical current to run through the circuits to power the fuses.
Next, turn your multimeter to DC mode. Connect the black terminal of your multimeter to the car’s chassis then use the positive terminal to test both sides of the fuse. If both sides of the fuse record 12V, then it’s good. However, if one side fails to show any voltage, then the fuse is faulty. This method is used to test fuses without removing them from the fuse box.
However, if you’re looking to remove the fuses from the fuse box to test them individually, then you can consider this method. First, set your multimeter to ohms (Ω) to test the resistance. Next, turn each fuse upside down to access the terminals. Using your multimeter’s probes, touch both terminals of your fuse and record the readings.
If the resistance reading ranges from 0 to 5 ohms, then it means the fuse is good. However, if the resistance reading is higher or the multimeter displays OL (Over Limit), then it means the fuse is faulty.
- Step Five: Replacing the Fuse
Now that you’ve detected and removed the damaged fuse, the last step in our discussion is to replace this fuse with a new one. Here, the size and amperage rating of the new fuse must be similar to the previous fuse.
Remember, a fuse with higher amperage will allow excess current to pass through which can damage your electrical components. On the other hand, a fuse with a lower amperage rating will prevent sufficient current from passing through thus causing it to blow.
Just to help you understand more about the amperage, here’s a table that outlines the color-coding of each fuse and its corresponding amperage rating.
| Color | Current/Amperage Rating |
| Black | 1A |
| Grey | 2A |
| Violet | 3A |
| Pink | 4A |
| Tan | 5A/70A |
| Brown | 7.5A |
| Red | 10A/50A |
| Blue | 15A/60A |
| Yellow | 20A |
| Clear | 25A/80A |
| Green | 30A |
| Orange | 40A |
Other than the colors, you need to be very keen on the sizes as they too play a critical role in choosing the exact replacement of your fuses. About the sizes, fuses are grouped into six main categories. They include:
- Micro2: Usually small with thin shapes
- Micro3: Easiest to identify as they have three terminals instead of 2
- Low-Profile Mini: These ones have short terminals that are close to the body
- Mini: Similar to low-profile mini only that the terminals are longer
- Regular: They’re the most common and have larger bodies
- Maxi: Largest sizes available and most suited for high current demands
FAQs
- Why Do Fuses Blow?
Fuses are tiny resistors that are tasked to protect your car’s electrical circuits from damage caused by an overflow of electric current. To do this, fuses have tiny metal wires inside that break whenever a high current passes through. This forces them to blow to interrupt the flow of electricity, which can damage your car’s electrical components.
- How Can You Prevent an Automotive Fuse From Blowing?
Although it’s hard to prevent your fuses from blowing, regular maintenance of your car’s electrical system is one sure-fire way of preventing this issue. You need to avoid leaving your charger connected to the cigarette lighter socket, as this is one major cause of blown fuses. You also need to inspect the condition of the wiring system to prevent any short-circuiting.
- Where Can I Buy a New Fuse?
Replacing a blown fuse is not a challenging process. The most difficult part is buying the right fuse that will be an exact match with the blown fuse. In our last step, we’ve mentioned that fuses come in different sizes and colors.
So, to get the specific match, you can buy the fuses online by keying in the exact specifications. You can also buy the fuses in any auto parts store or a well-stocked auto service station.
Conclusion
As you can see, telling whether an automotive fuse is blown is usually a simple process. All you need is to locate the fuse box, inspect the fuses, test them using a test light or a multimeter and then replace the faulty fuse.
But, despite being a simple process, your car’s fuse cannot blow without a valid reason. In case you install a new fuse and it blows soon after, then it’s clear your car has a severe electrical problem. In this case, it’s recommended that you seek expert help from a professional mechanic.
