When your phone charger stops working, the dome light won’t come on or the wipers suddenly quit, the first thing to check is a fuse. Car fuses are cheap, easy to replace and designed to fail on purpose, protecting the wiring and electronics from an overload. Knowing how to find and swap one can save a trip to the shop and get you back on the road in minutes.
What a car fuse does
A fuse is a small strip of metal inside a plastic or glass housing. Each one is rated for a certain current, measured in amps. If a circuit draws more current than the fuse is rated for, because of a short circuit or a faulty part, the metal strip melts and breaks the circuit before the wiring can overheat. That’s why a fuse that blows is usually a symptom: it did its job, and something on that circuit asked for too much power.
Where to find the fuse boxes
Most cars have at least two fuse boxes, and some have three:
- Inside the cabin, often under the dashboard on the driver’s side, behind a panel at the end of the dashboard, near the driver’s knee or behind the glove box. This box usually covers interior items like power outlets, the radio, interior lights and power windows.
- Under the hood, in a black plastic box near the battery. This one tends to hold higher-current fuses and relays for things like the cooling fan, headlights, horn and starter circuits.
- In the trunk or under a seat on some vehicles.
Your owner’s manual shows exactly where each box is and which fuse protects which circuit. There’s usually a diagram printed inside the fuse box lid as well. Many fuse boxes also have a small plastic fuse puller and a few spare fuses clipped inside the lid.
Types of car fuses
Most modern cars use blade fuses, which have two metal prongs and a colored plastic body. They come in several sizes, so the replacement has to match the one you remove:
- Micro fuses are the smallest and are common in newer cars.
- Mini and low-profile mini fuses are slightly larger and very common.
- Standard blade fuses are the classic size found in many cars from the past few decades.
- Maxi fuses are large blade fuses for high-current circuits, usually under the hood.
Older and classic cars may use glass tube fuses, and some high-current circuits use bolt-in or cartridge-style fuses that are best left to a mechanic.
Fuse color codes
Blade fuses are color-coded by amp rating, and the number is also printed on top of the fuse. Common ratings include:
- 5 amp: tan
- 7.5 amp: brown
- 10 amp: red
- 15 amp: blue
- 20 amp: yellow
- 25 amp: clear or natural
- 30 amp: green
Always go by the number on the fuse and the rating in your fuse diagram rather than color alone.
How to tell if a fuse is blown
Start by finding the fuse for the circuit that stopped working, using the diagram. Then:
- Turn off the ignition and the item that isn’t working.
- Pull the fuse straight out with the fuse puller or a pair of needle-nose pliers.
- Look at it against the light. In a blade fuse, the metal strip you can see through the plastic should be one unbroken piece. A blown fuse has a visible gap, and sometimes the plastic is darkened or melted.
- Test it if you can’t tell. Many blade fuses have two small metal test points on top. With a test light or multimeter, you can check for continuity across the fuse, or check both test points with the ignition on while the fuse is still in place. A good fuse shows power on both sides; a blown fuse shows power on only one.
Fuse boxes tend to be in dark corners, so a bright light makes this much easier. A rechargeable LED work lamp you can set down in the footwell leaves both hands free.
How to replace a blown fuse
- Get the right replacement. It must be the same type and size, and exactly the same amp rating as the fuse you removed and the rating shown in the diagram.
- Make sure the ignition is off.
- Push the new fuse firmly into the empty slot until it’s fully seated.
- Turn the ignition on and test the item that wasn’t working.
- Put the lid back on the fuse box, and replace any spare you used so you have one next time.
Never use a higher-rated fuse
It can be tempting to put in a bigger fuse if one keeps blowing, or to borrow one from another slot, but a fuse rated higher than the circuit is designed for can let the wiring overheat before it blows. That’s a fire risk. Never bridge a fuse slot with foil or wire either.
When a fuse keeps blowing
A fuse that blows again right away, or every few days, is a sign of a fault on that circuit. Common causes include:
- A short circuit where a wire has rubbed through its insulation and is touching metal.
- A faulty device, such as a failing motor in a power window or a damaged charger in the power outlet.
- Aftermarket accessories, like extra lights or a dash camera, wired into a circuit that can’t handle the load.
- Water getting into connectors or the fuse box.
Unplug anything plugged into the circuit and try a new fuse. If it still blows, have an auto electrician or mechanic trace the fault. Electrical problems that seem minor can lead to bigger trouble if they’re ignored.
Related electrical fixes
If your headlights are the problem, our guide to fixing dim, foggy or burned-out headlights walks through bulbs, wiring and aiming. If the car won’t start at all, the cause is more likely the battery than a fuse; see how to use a car battery charger safely. And for the basic tools worth keeping on hand, see our guide to automotive tools for your home garage.
FAQ
Can I drive with a blown fuse?
It depends on what it protects. A blown fuse for a power outlet is an inconvenience, but one for headlights, wipers, brake lights or the fuel pump affects safety or stops the car. Replace it before driving if it’s safety-related.
Why did my car fuse blow for no reason?
Fuses blow for a reason, even if it isn’t obvious. Sometimes it’s a one-time surge or a faulty plug-in device. If it happens again, there’s likely a fault in the circuit.
Are all car fuses the same?
No. They differ in size, type and amp rating. Always match the replacement to the original and to your owner’s manual.
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