How do I find and change a fuse in a car?
Where the fuse boxes actually are, how to read the diagram, how to spot a blown fuse, and why a fuse that blows repeatedly is telling you something the fuse cannot fix.
- Difficulty
- beginner
- Time
- 20 min
- Read
- 5 min
- Safety
- caution
Short answer
Cars usually have two or three fuse boxes: one under the bonnet, one in the cabin behind a panel at the end of the dashboard or in a footwell, and sometimes one in the boot. The lid carries a diagram and a puller. A blown fuse has a visibly broken metal strip inside. Replace it with exactly the same amp rating — the number is stamped on it and matched by its colour. If it blows again, there is a short, and the fuse is doing its job by refusing to be the last line of defence.
A fuse is a deliberate weak point. It is a thin strip of metal chosen to melt before the wire behind it does, so that a short circuit ends in a fifty-pence part rather than a burnt loom. That is worth holding onto, because it explains everything about how to treat them: the fuse is not the fault, it is the evidence of one, and making it stronger only moves the failure somewhere much more expensive. Changing one is genuinely a two-minute job that saves a diagnostic fee when a single item stops working — one window, the cigarette lighter socket, the rear wiper, the radio.
Safety
Step by step
- Confirm it is likely to be a fuse at all.Fuses protect circuits, so a fuse fault usually kills everything on that circuit at once and completely. One dead item that shares a fuse with three working ones is probably not the fuse. Everything on the dashboard dying at once is more likely a battery or earth problem.
- Find the fuse boxes.Almost every car has one in the engine bay, in a black plastic box with a clipped lid, and one inside the cabin — commonly behind a pop-off panel at the end of the dashboard visible only with the door open, in the driver's or passenger's footwell, or behind the glovebox. Some cars add a third in the boot near the battery.
- Read the lid.The inside of the lid, or a card clipped to it, maps every position and what it protects. If it is missing or unreadable, the handbook has the same table, and manufacturers publish it online by registration.
- Switch the ignition off before you pull anything.Removing a fuse from a live circuit can arc and can upset control modules. Key out, and on a keyless car make sure the system has actually gone to sleep.
- Pull the fuse with the plastic puller, not pliers.There is usually a small plastic puller clipped inside one of the boxes. Metal pliers can bridge two terminals. Pull straight out rather than levering sideways, which cracks the holder.
- Look at the metal strip through the plastic.A healthy fuse has an unbroken S-shaped strip. A blown one has a visible break or a sooty smear. Hold it up to the light — some breaks are hairline. If you cannot tell, a cheap circuit tester or a multimeter on continuity settles it.
- Replace it with exactly the same rating.The number stamped on top is the rating in amps, and the colours are standardised: on the common blade type, 5A is tan, 7.5A brown, 10A red, 15A blue, 20A yellow, 25A clear or white, 30A green. Match the number, not just the colour, and keep a small assortment in the glovebox.
- Test before you close everything up.Turn the ignition on and try the item. If it works, done. If the new fuse blows immediately, stop — you have a short circuit, and the next step is a garage rather than another fuse.
Common mistakes
- Fitting a bigger fuse because the small one keeps blowing — The fuse protects the cable. A 30A fuse in a 10A circuit lets the wire cook quietly inside the loom until the insulation fails. It is the single most dangerous thing anyone does with car electrics.
- Assuming a working item means a good fuse — Some circuits are protected twice, and some fuses feed several things. Reading the lid diagram rather than guessing saves pulling fifteen fuses.
If it doesn't work
The same fuse blows again straight away
Cause: A short to earth somewhere on that circuit — a chafed cable, a water-damaged connector, or a failing motor drawing too much — Fix: Stop replacing it. Note which circuit it is from the lid diagram and hand that to the garage; naming the circuit turns an expensive hunt into a targeted one.
Fuse blows only sometimes, usually over bumps or in rain
Cause: An intermittent short from a chafed loom or water ingress — Fix: The hardest kind to find and the most worth describing precisely. Note exactly when it happens — rain, bumps, full lock, tailgate open — because that pattern points at where the loom flexes or gets wet.
Fuse is fine but the item still does not work
Cause: A relay, a switch, an earth point or the component itself — Fix: Relays sit in the same boxes and often several identical ones are fitted; swapping a suspect relay with a known-good identical one is a legitimate free test. Beyond that it is a diagnosis job.
Several unrelated things stopped working at once
Cause: A shared earth point corroding, or a main fuse or fusible link in the engine bay box — Fix: Look for the large high-current fuses in the engine bay box. A corroded earth strap between engine and body is also a classic and cheap cause of strange multiple faults.
Fuse box is full of water or green corrosion
Cause: Blocked scuttle drains, a leaking seal or a windscreen leak — Fix: Fix the water before the electrics. The catalogue's guide on a wet car carpet covers the drains that cause most of it.
Questions people ask
Are car fuses all the same?
No. The common standard blade fuse comes in mini, standard and maxi sizes, and older cars used continental or glass fuses. Newer cars also use low-profile mini blades and, for high-current circuits, bolt-in fuses that are not a roadside job. Buy an assortment that matches what is actually in your car.
Can a blown fuse drain my battery?
Not by itself, but the fault that blew it might. A partially shorted circuit can draw current with the ignition off, and that is one of the standard causes of a car that goes flat over a few days.
Where do I find the diagram if the lid is missing?
The handbook has it, and most manufacturers publish handbooks online free by model and year. Owners' forums for your specific car are also reliable for this, because it is factual and easy to verify against your own box.