The quickest way to check if a fuse is bad is a visual inspection (for glass fuses) or a simple continuity test with a multimeter. Either method takes less than a minute, and you don’t need any special training. The approach depends on the type of fuse you’re dealing with, whether it’s a glass tube in an appliance, a colored blade fuse in your car, or an opaque ceramic cartridge you can’t see through.
Start With a Visual Check
If your fuse has a glass body, you can often diagnose it with your eyes alone. Hold the fuse up to a light and look at the thin wire running through the center. A good fuse has an unbroken wire connecting both metal end caps. A blown fuse will have a visible gap in that wire, or you’ll see a dark, metallic smear on the inside of the glass where the wire vaporized. Either sign means the fuse is dead and needs replacing.
This method doesn’t work for ceramic cartridge fuses, which have an opaque body that hides the filament. For those, you’ll need a multimeter.
How to Test a Fuse With a Multimeter
A basic digital multimeter is the most reliable way to confirm whether any fuse is good or blown. You have two options: a continuity test or a resistance test. Both tell you the same thing.
Continuity Test
Turn your multimeter’s dial to the continuity setting, which is usually marked with a small diode symbol or the word “CONT.” Touch one probe to each metal end of the fuse. It doesn’t matter which probe goes on which end. If the fuse is good, the multimeter will beep, meaning electricity can flow through. No beep means the internal wire is broken and the fuse is blown.
Resistance Test
If your multimeter doesn’t have a dedicated continuity mode, switch the dial to the resistance setting, marked with the Greek omega symbol (Ω). Touch one probe to each end of the fuse, making sure you have solid contact with the metal caps. A good fuse reads very low resistance, near zero ohms. A blown fuse displays “OL” (overload) or infinite resistance, meaning no current can pass through. Anything above about 1 ohm on a standard fuse is suspicious and likely means it’s failed.
Testing Automotive Blade Fuses
The colored blade fuses in your car’s fuse box follow the same testing principle. Pull the fuse out using the small plastic fuse puller that’s usually clipped inside the fuse box lid, then touch your multimeter probes to the two metal blades. A beep on continuity (or near-zero resistance) means it’s fine. No beep or “OL” means it’s blown.
Many blade fuses are also semi-transparent, so you can visually check the tiny wire bridge between the two blades. A broken or melted bridge is an obvious fail. If the plastic housing looks discolored or scorched, that’s another giveaway.
Blade fuses are color-coded by amperage. Some of the most common ratings you’ll encounter: tan is 5A, red is 10A, blue is 15A, yellow is 20A, and green is 30A. When you replace a blown fuse, match the color and amperage exactly. The color code matters because installing a higher-rated fuse defeats the fuse’s purpose as a safety device. Without proper overcurrent protection, wiring can overheat, melt its insulation, and start a fire.
Testing a Dryer or Appliance Thermal Fuse
If your dryer runs but doesn’t heat, or won’t start at all, a blown thermal fuse is one of the most common causes. Thermal fuses are one-time safety devices that trip permanently when they detect excessive heat. They look like small plastic or metal capsules with two wire terminals, and they’re typically mounted on the blower housing or near the heating element.
To test one, unplug the dryer first, then access the fuse by removing the back panel (check your owner’s manual for the exact location). Disconnect the wires from the fuse terminals, set your multimeter to continuity or the lowest resistance setting, and touch a probe to each terminal. A beep or a reading near zero ohms means the thermal fuse is intact. No beep or infinite resistance means it’s blown and needs to be replaced. Unlike standard fuses, thermal fuses can’t be reset. A new one is the only fix.
Safety Before You Start
Always disconnect the power source before removing or handling a fuse. For household appliances, unplug them from the wall. For your home’s electrical panel, switch off the main breaker before pulling cartridge fuses. Federal electrical safety standards prohibit removing or replacing fuses by hand in an energized circuit, and for good reason: live circuits carry enough current to cause serious injury.
For automotive fuses, turning off the ignition is sufficient. Use the plastic fuse puller rather than your fingers to avoid bending the blades or cutting yourself on the tight fuse box slots.
What to Do After Finding a Blown Fuse
Replacing a blown fuse is straightforward: match the amperage rating exactly and insert the new fuse. But a blown fuse is a symptom, not the root problem. The fuse blew because something drew more current than the circuit was designed to handle. If the new fuse blows immediately or within a short time, you’re dealing with a short circuit or a failing component somewhere on that circuit.
For cars, a repeatedly blown fuse often points to a faulty motor, a pinched wire, or a malfunctioning accessory on that circuit. For home appliances, it could be a worn-out heating element, a seized motor, or damaged wiring. One blown fuse is normal wear and tear. Two in a row means something else needs attention.