Testing car fuses is one of the most straightforward DIY repairs any vehicle owner can do. You only need a test light, multimeter or voltmeter to check for continuity, but you can also examine the fuse visually for any signs of damage if you have no tool.
Check our detailed guide below, including the steps to replace a bad fuse without putting various car electrical components at risk of damage. Also, we will give you a few tips to prevent fuses from blowing out prematurely.
- 1 How To Check Whether Your Auto Fuses Are Good?
- 2 How To Replace a Blown Car Fuse Safely?
- 3 How To Prevent Your Auto Fuses From Constantly Blowing?
- 4 Frequently Asked Questions
- 5 Conclusion
- 6 References
How To Check Whether Your Auto Fuses Are Good?
To check whether your auto fuses are good, inspect them visually one by one for any signs of damage. If you need to be sure, check for continuity using a multimeter or voltmeter. You can also buy a test light for a few bucks at most auto parts stores.
A blown auto fuse can present itself in many ways. The most common symptoms are when an electrical component randomly stops working. In the worst-case scenario, the vehicle can fail to start, depending on which fuse is damaged. If you’ve encountered a similar situation, then it’s likely that one of your fuses has blown out.
Fortunately, anyone with a basic understanding of electrical circuits can test and replace damaged auto fuses as it involves minimal disassembly. To get started, you must locate the fuse box where the various fuses are contained. Different vehicles have their boxes placed in various locations. Please consult your owner’s manual.
Typically, modern vehicles have two fuse boxes: one inside the cabin, under the dash, near the steering wheel and the other under the hood. Remove the cover once you locate the box, and you’ll find the fuse map. The various blade fuses will be grouped based on their current rating (in amps). If nothing is printed on the cover, check your owner’s manual.
The next step will be to test the fuses using one of the methods above.
See more in length below.
Inspect the Fuse Visually
The easiest way to check automotive fuses is by visual inspection. Fuses have a thin metal strip that melts when the flowing current exceeds the fuse rating. Since the fuse is made of transparent material, it’s easy to see when this metal strip is melted or broken. First, unplug the fuse to observe it.
There’s usually a tool for unplugging the fuses inside the box. You remove a fuse by pulling it straight up gently to avoid damage. Once you’ve removed the fuse, look at it keenly for any visible signs of damage, e.g., burns. If you can see a metal conductor running through it, it’s not blown.
But if there’s a visible gap in the wire or metallic smear inside the glass, the fuse is blown and needs replacement. One disadvantage of this method is that you must remove and check one fuse at a time, which can be time-consuming.
Check With a Digital Multimeter
This is the go-to method for those wondering, “How to check fuses without removing them?” or “How to test fuse box with multimeter?” There are two ways to examine fuses with the meter. One involves measuring the voltage at both blades (pins) of the fuse. Small auto fuses have pins protruding at the top, allowing one to measure the voltage without pulling them out.
Turn on the ignition to power all the fuses and ensure the parking brake is engaged. Check the voltage on either side of each fuse using the positive probe. Your fuse is good if both sides read 12 volts and blown if one side shows 12 volts while the other shows no voltage. This method allows you to check multiple fuses in the shortest time possible.
The other way is to perform a continuity test when the fuse is pulled out. In this case, you’ll check the fuse resistance (opposite of current flow). A lower resistance indicates a higher current flow. Resistance is measured in Ohms (Ω).
To learn how to test a 30 amp fuse with a multimeter, switch off the engine and unplug the fuse. Set the meter to Ohms and connect the positive and negative leads to the fuse pins. A multimeter reading of zero or a number close to zero Ohms means that the fuse is good or there’s a continuity between the two pins of the fuse. Otherwise, the reading will show a very high resistance (infinity).
Use a Voltmeter
You can also use a voltmeter for testing fuses in your car. Voltmeters come in handy when one only requires voltage measurement, unlike a multimeter, which can measure different electrical quantities at the same time, such as voltage, current, and resistance. Learning how to check if a fuse is getting power with a voltmeter is straightforward.
Turn on the ignition and set your meter to the 20-volt scale. Next, touch the negative probe of the voltmeter to the battery’s negative terminal and the positive one to each of the metal pins on the fuse. The fuse is good if the meter displays a reading of 12 volts on both pins. A voltmeter is an excellent option if you’re wondering how to check big fuses in car.
Do a Replacement Test
Another answer to “how to check a car fuse without a multimeter?” is a replacement test. It’s generally a trial-and-error method and involves replacing the particular fuse you suspect to be blown with a good one. Before you do that, ensure the engine is off.
After replacing the fuse, turn the ignition back on and check to see if the new fuse is working. If it does, you’ve found the blown fuse, but if not, repeat the steps for another fuse until you eliminate all the culprits.
Electrical Tester Pen
An electrical or fuse tester pen (test light or non-contact tester pen) is a fast, accurate and safe tool for measuring current at the fuse box. It’s an excellent choice for fault-finding on cars’ electrical circuits. As the name suggests, the tester looks like a pen with a built-in sensor at the tip that detects the voltage presence when it touches a conductor or electrical outlet.
How to check car fuses with test lights? You hold the tool and act like the ground reference through ‘capacitive coupling.’ Next, touch the tip of the pen to the fuse pins. When the pen detects voltage, the tip glows red, and the tool may also beep.
An excellent example of a test light is the Bussmann ft-3 fuse tester/fuse puller, perfect for testing blade fuses. The tool is also used to remove fuses safely. Another one is the Sealey TA120 current tester 20A. You can buy any of them online for a few bucks.
How To Replace a Blown Car Fuse Safely?
To replace a blown car fuse safely, buy the correct fuse for replacement, one whose amperage rating coincides with the damaged fuse. Next, turn off the engine and disconnect the battery. Plug in the new fuse, reconnect the battery and turn the engine back on to test it.
Buy the Correct Replacement Fuse
The most crucial step in replacing auto fuses is buying fuses with the correct amperage rating. It would be best if you didn’t replace a 30-amp fuse with a 10-amp one because that will cause the fuse to blow as soon as you replace it.
Replace a 30-amp fuse with a new 30-amp fuse to avoid trouble. You’ll usually find the information on the power required for each fuse printed on the fuse’s glass container, the label attached to the fuse or the box cover.
Disconnect the Battery
You should turn the engine off and disconnect the battery when changing fuses on your car. It’s essential to cut off power when performing any electrical work. A misstep with your automotive wiring, while the battery is hooked up, could result in severe damage to the various electrical systems. You disconnect the battery by removing the negative terminal.
Plug in the New Fuse and Test
With the engine off and the battery’s negative terminal removed, pull out the damaged fuse and plug in the good one. Next, reconnect the battery and start the ignition to test the fuse. The fuse should work if nothing else is the problem. Otherwise, consider contacting an expert for an accurate diagnosis and repair.
How To Prevent Your Auto Fuses From Constantly Blowing?
To prevent your auto fuses from constantly blowing, fix a potential short circuit problem commonly triggered by frayed wire insulation, malfunctioning electrical components or fluid leaking on a wiring harness and connection points. When replacing blown fuses, use new ones with the correct amperage rating.
Fix a Potential Short Circuit Problem
A short circuit in one of your car’s electrical systems will cause a fuse to blow. Fixing a short is easy once you identify the problem’s location. Common causes of short-circuiting include wire insulation fraying. If one or more wires are frayed and exposed, it can cause a short when it touches the car’s metal frame (ground).
Also, the exposed wire might constantly move around and occasionally come into contact with the metal surface, causing interment shorts. That means the fuse gets blown every soon after replacement.
Short-circuiting can also be triggered by a malfunctioning device. For example, internal damage to a windshield wiper motor can cause the wiper system to use more current than necessary. If that happens, it will overload the circuit leading to a short.
Another common cause of shorts is a fluid leak, which can get a wiring harness and connection points. Wet conductors are more susceptible to short-circuiting. So, carefully find the root of the short and fix it or call an expert for help.
Always Ensure Proper Replacement of Fuses
A fuse works as a circuit breaker. Thus, it will blow if you use one with incorrect amperage. Auto fuses come in varying amperage and material, depending on their application. Whenever replacing a failed fuse, ensure you only use the correct one.
If you can’t find any information on the box cover, look in your owner’s manual or ask a professional. Although replacing a fuse is easy and inexpensive, it’s not something you want to do every time. So, ensure you do the right thing.
Frequently Asked Questions
What Is the Lifespan of a Typical Auto Fuse?
The lifespan of a typical auto fuse is 10 years. Failing electrical components in the vehicle, manufacturing faults, and wrong installations can lead to premature fuse blowing. Luckily, fuses are one of the most straightforward and inexpensive auto parts to replace, and anyone can do it without expert help.
Is Blowing the Only Way Auto Fuses Can Go Bad?
No, blowing is not the only way auto fuses can go bad. In rare cases, a break can happen at the metal strip on the terminals inside the fuse because of excessive vibrations or manufacturing defects. Moisture exposure can also cause a fuse to defect without necessarily blowing.
After reading our guide above, testing car fuses won’t be a difficult thing anymore.
We will leave you with a summary:
- The easiest way to examine fuses is by visually inspecting them, which doesn’t require any tools.
- A multimeter or voltmeter can also help determine if a fuse is blown.
- You can also use a test pen if you don’t have a digital multimeter or voltmeter.
- When changing a fuse, disconnecting the battery is essential to prevent damage to your electrical components.
- You can prevent your fuses from blowing constantly by fixing a possible short circuit and replacing damaged fuses correctly.
You now have the knowledge you need to find and replace damaged fuses in your car. So, choose your best method, do the fuse testing, and consult an expert if you need further assistance.
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