How do you check whether a fuse is blown?
Something electrical stopped working. Before you touch anything expensive, spend ninety seconds on the cheapest suspect in the car.
Applies to
- Process
- Automotive electrical diagnosis
- Materials
- Glass and blade (ATO/ATC/mini) fuses
- Setup
- Fuse puller, phone flashlight, multimeter or test light
- When
- First step on any dead circuit
Why it matters
A fuse is the cheapest part in the circuit and it's designed to be the thing that fails. Checking it first stops a lot of people replacing a switch, a motor, and then the fuse anyway.
The blown ones aren't always obvious. A hairline break in the link reads as intact until you get light behind it, and a slow-blow that's been cooking looks cloudy rather than broken.
What good looks like
- The link is one continuous strip with light behind it
- No dark smoke or cloudy film inside the body
- Continuity beeps across the two contacts
How to apply it
- Pull the fuse with a puller, not pliers — pliers crack blade fuses.
- Backlight it with a phone flashlight and look at the internal link.
- If you can't call it, put a meter on continuity across the two caps or blade tips.
- Replace like for like — same amp rating, always. Never a higher one.
Exceptions & tradeoffs
A fuse that blows again immediately is telling you something. Don't keep feeding it fuses; find the short.
Never substitute a higher-rated fuse to "stop it blowing". The fuse is protecting wiring that's sized for that rating, and the next failure won't be the fuse.
Common mistakes
- Judging a fuse by eye in a dim engine bayGet light behind it, or use a meter
- Fitting a 20 A where a 10 A wasMatch the original rating exactly — that's a wiring fire otherwise
Inspecting the fuse link and confirming with a continuity check — Test A Fuse?! Nooo Waaay! ↗ at 0:17–0:40.
Summarized and independently edited by Start Here. The clip appears to show a phone-based check but the exact trick wasn't clearly visible in the frames, so what's written here is the general inspect-then-continuity method rather than the creator's specific move. Worth confirming against the video before relying on it.