Former User

If you suspect a fuse is blown, use the method described below in the diagrams.

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Possible test outcomes:

1) Battery voltage (~12.5V) is measured on both test tabs of the fuse.

This indicates that the fuse receives voltage from the battery and that the fuse is not blown. However, if the voltage is not almost identical on both test tabs, the fuse is bad and should be replaced.

2) Battery voltage (~12.5V) is measured on only one of the two test tabs of the fuse.

This indicates that the fuse receives voltage from the battery but that the fuse is blown. Replace the fuse and repeat the test.

3) Battery voltage (~12.5V) is measured on neither of the two test tabs of the fuse.

This indicates that the fuse does not receive voltage from the battery, but does not tell you whether or not the fuse is blown. Identify problem in the circuit that prevents voltage from the battery from reaching the fuse.


(Click here to learn how to do other basic electrical tests.)


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The Method

92lxsleeper

why not just set it to continuity? and if it beeps its good, if not then its blown. you can check fuses regardless if they have power going to them or not

teggi

never trust it. always volt drop.

Former User

If done correctly, a continuity test should indeed reliably test for a blown fuse. But the voltage test I describe gives the same information plus it additionally tells you whether the fuse receives and transmits battery voltage as it should. Therefore, doing the voltage test gives twice the information of the continuity test for the same amount of work.

Former User

Good point. Thanks. I added this^ to the Possible Test Outcomes section.

moaterboaink1ng

Very helpful. Thanks I was just doing a visual inspection.

prboy1969

Simple, and great guide. Thanks.

TiNuts

I know this is old, but any voltage drop/change across a fuse will only happen if its under load and will change depending on the load. ie: let's say a headlight fuse (for examples sake)has started to open, but hasn't blown completely, with the headlights on you may measure a noticeable drop across the fuse. With the headlights off, there will be no drop (no current through the fuse). You could then take this same fuse and put in the dome light circuit. Because the dome light pulls much less current than the headlights, you will not measure the same voltage drop across the fuse as you would with it in the headlight circuit. The continuity test will at least put a small amount of load through the fuse (but probably not enough to actually measure). It is certainly trustworthy enough to determine if a 12v fuse is bad or not.

Plus, it's very quick since you don't have to keep looking down at your meter if you are checking a number fuses, and it doesn't matter if the circuit is powered and/or on/off.

NotAJDMFanBoy

setting the meter to continuity and running power through it can blow it. I did that once..., it's all good though, it was a junky meter and an excuse to get a $15 digital Craftsman one I like better.

Fuses out of the car, continuity test. Fuses in the car, test DC Voltage.