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September 12, 2023

How to Tell If a Fuse is Blown

Whether it's your car's power windows, heater or stereo, if an electronic fails to turn on it may be due to a simple cause like a fuse being blown. But before you go out and buy a replacement, first you need to know how to tell if a fuse is blown.

Electrical fuses serve an important purpose: to cut off current from a circuit when there's too much electricity passing through it. This can be caused by wires touching each other, misdirected live wiring or too many devices drawing electricity from a single outlet. Blown fuses are a common sign that there's an issue with a specific circuit and it will be helpful to diagnose the problem to find an appropriate fix.

A common tool to help with this is a multimeter. These handy devices are capable of measuring voltage, current and resistance among other things. If you're not comfortable using a multimeter, most electrical fuse types offer visual pointers that make it easy to see if they are blown. Plug fuses found in most home fuse boxes have threaded terminals that look a little bit like light bulb ends, so it's fairly easy to test them with a multimeter by running a continuity test between the two terminals.

To do this, first remove the fuse from its holder and hold it up to the light. If you see a gap in the filament, dark stain or a metal smear it is blown and needs to be replaced. Now, set your multimeter to the resistance or "OL" setting and touch one of the leads of the multimeter to each end of the fuse. If the reading on the display reads infinite resistance, then it's definitely blown and will need to be replaced.