What a multimeter tells you about a fuse
A multimeter is a handheld device that measures electrical properties. When you hold the meter's probes against a fuse, it tells you whether electricity can flow through it — which means the fuse is good — or whether the circuit is broken, which means the fuse has blown and needs replacing.
You do not need to remove the fuse from its holder to test it. You can touch the probes directly to the metal ends of the fuse while it sits in place. This is safer than pulling it out, because you avoid touching live metal parts and you can see exactly which fuse you are testing.
A multimeter costs between $15 and $50 for a basic model that works for household fuses. You will use the continuity setting, which is the fastest way to check whether a fuse is open or closed.
Key Takeaways
- Set your multimeter to continuity mode (usually marked with a sound-wave symbol) before you touch the probes to the fuse.
- Touch one probe to each metal end of the fuse — the meter will beep or show a reading if the fuse is good, and stay silent or show infinity if it is blown.
- Test the fuse while it is still in the holder to avoid touching live parts and to confirm you are testing the right one.
- A blown fuse looks dark or has a broken wire visible inside the glass, but a meter test is more reliable than looking.
Setting up your multimeter for a fuse test
Turn the multimeter's dial to the continuity setting. On most meters, this is marked with a symbol that looks like a sound wave or musical note. Some meters label it as "Ω" (ohms) with a small arrow or dot next to it. If you cannot find continuity, the resistance setting (ohms) works the same way for fuses.
Make sure the meter is powered on. Most multimeters have an on/off switch, though some turn on automatically when you turn the dial. Check that the two probe wires are plugged into the correct ports — the black probe goes into the port marked COM (common), and the red probe goes into the port marked V, Ω, or mA. If the probes are in the wrong ports, the meter will not work.
How to touch the probes to the fuse
Locate the fuse you want to test. Fuses are usually housed in a plastic box under the hood of a car, in a panel inside a house, or in a small holder on an appliance. Each fuse has two metal ends — one on top and one on the bottom, or one on each side.
Hold the black probe against one metal end of the fuse. Hold the red probe against the other metal end. Press firmly enough that both probes make solid contact with the metal, but do not force them. You should hear a beep or see a number appear on the meter's screen within a second or two.
If the meter beeps or shows a number close to zero, the fuse is good — electricity can flow through it. If the meter stays silent and shows "1" or "infinity" on the screen, the fuse is blown and needs to be replaced.
What the meter readings mean
A beep is the clearest sign that a fuse is working. When the meter beeps, it means the circuit is complete and current can pass through. You can stop testing and move on.
A number close to zero (usually between 0 and 5 ohms) also means the fuse is good. The exact number depends on the fuse's resistance, but anything in that range indicates a working fuse.
A reading of "1" or "infinity" means the fuse is blown. The circuit is broken, and no current can flow. This fuse must be replaced with one of the same amperage rating.
If the meter shows no reading at all and does not beep, check that both probes are touching the metal ends of the fuse firmly. If you still get no response, the meter may not be set to continuity mode, or the probes may be in the wrong ports.
Testing a fuse versus replacing it
A blown fuse often looks different from a good one — the wire inside the glass may be broken, or the glass may be dark or discolored. However, appearance is not always reliable. A meter test is the only way to be certain.
If the meter shows the fuse is blown, you will need to replace it. Turn off the power to the circuit or device before you pull the old fuse out. Insert a new fuse of the exact same amperage — the amperage is printed on the fuse's body. Do not use a fuse with a higher amperage, because it will not protect the circuit if something goes wrong.
If the meter shows the fuse is good but the circuit is still not working, the problem is somewhere else — in the wiring, a switch, or another component. A meter test only tells you about the fuse itself.
Common mistakes when testing fuses
The most common mistake is forgetting to switch the meter to continuity mode. If you leave it on voltage mode or resistance mode, you will get confusing readings that do not tell you whether the fuse is good. Always check the dial before you start.
Another mistake is not pressing the probes firmly against the metal ends. If the contact is loose, the meter may not beep even though the fuse is good. Press until you feel the probe tips make solid contact.
Some people test a fuse and then assume it is the problem without checking anything else. A blown fuse usually means something else in the circuit has failed — a short circuit, a failed component, or a wiring problem. If you replace the fuse and it blows again immediately, stop and find out why before you replace it a second time.
When to test a fuse versus when to just replace it
If you have a spare fuse of the correct amperage and the circuit is not working, it is often faster to replace the fuse first and see if that fixes the problem. Testing takes a few minutes, but so does replacing a fuse.
Testing is more useful when you want to know which fuse is the problem without replacing several, or when you are not sure whether a fuse is blown or whether the problem is elsewhere. A meter test gives you that information in seconds.
Testing is also the right choice if you are troubleshooting a circuit that keeps failing. If you replace a fuse and it blows again, test the new fuse to confirm it is actually blown, then investigate what is causing the circuit to fail.
Frequently Asked Questions
Can I test a fuse while the power is on?
Yes. Testing a fuse with a multimeter on continuity mode is safe even when the circuit is powered. The meter draws almost no current, so it will not be damaged. However, if you are going to replace the fuse, turn off the power first.
What if my multimeter does not have a continuity setting?
Use the resistance (ohms) setting instead. A good fuse will show a reading close to zero ohms. A blown fuse will show a very high number or "infinity." The continuity mode is faster because it beeps, but the ohms setting gives you the same information.
Do I have to remove the fuse to test it?
No. You can test a fuse while it is in the holder by touching the probes to the metal ends. This is actually safer and easier than pulling it out, because you avoid touching live parts and you can see which fuse you are testing.
What amperage fuse should I use as a replacement?
Use the exact same amperage as the blown fuse. The amperage is printed on the fuse's body — common ratings are 5A, 10A, 15A, 20A, and 30A. Using a higher amperage fuse will not protect the circuit if something fails, and using a lower amperage fuse will blow repeatedly.
Why did my fuse blow in the first place?
A fuse blows when too much current flows through the circuit. This usually means a device has failed, a wire is damaged, or something is plugged into the wrong outlet. If a fuse blows more than once, the circuit itself has a problem that needs to be fixed, not just the fuse replaced.