Sometimes you can inspect a fuse just by looking at it. A cartridge fuse may be blackened and distorted, the contact terminals may be arced and burned, or the body may have disintegrated. With plug-type fuses, look at the window to see if the element is broken or blackened. Many times a fuse element looks good when it isn’t. As a double-check, use a multimeter or a similar device.
How to test a fuse with a multimeter?
A multimeter uses two probes to check a fuse. It sends a low-amperage current into one end of the fuse (via one probe); if the current comes out the other end of the fuse and enters the second probe, the fuse is considered good. The multimeter indicates this by a tone, light, or numbered reading, depending on the device.
The fuse multimeter has two types of testers: a continuity tester (where it is set now) and ohms, or resistance, tester (two positions to the right). To use the device, place a probe on each fuse contact (it doesn’t matter which probe goes on which contact). The continuity tester sounds a tone and the resistance tester provides a resistance reading (close to zero). If you do not receive an immediate continuity indication, scratch the probe into the contact’s metal to bypass any corrosion.
To do a continuity check on a cartridge fuse, place a probe on each of the fuse’s metal end caps. Sometimes the caps come loose as the fuse body distorts.
To check a knife-blade fuse, place a probe on each blade.
A type-S fuse needs a probe on the center terminal and a probe on the metal band below the threads.
A plug fuse’s terminals are the screw threads and the center terminal. Place a probe on each one.