What Is a Fuse?
A fuse is a deliberately weak link in an electrical circuit. It contains a thin strip of metal that melts and breaks the circuit when the current flowing through it exceeds a safe level. This protects the wiring and components downstream from overheating, catching fire, or being permanently damaged.
Think of it as a sacrificial device — a fuse "blows" (fails) on purpose so that the wiring harness does not overheat.
Modern cars contain 30–80 or more fuses, each protecting a specific circuit or group of circuits.
Where Is the Fuse Box?
Most NZ vehicles have two or more fuse boxes:
Underbonnet fuse box (engine bay, near the battery) — high-current fuses protecting major systems (cooling fan, ABS, fuel pump, engine management, alternator)
Interior/passenger compartment fuse box — usually located:
- Behind a panel on the driver's side dashboard (look for a cover with a small notch)
- Under the steering column
- In the glovebox
- Under the driver's or passenger's seat
Some vehicles have a third fuse box in the boot.
Your owner's manual has a fuse box diagram — this is the definitive reference for your specific car. It shows which fuse number protects which circuit, and the correct amperage for each fuse. The fuse box lid often has a partial diagram printed on its inside face.
Types of Fuses in NZ Cars
| Type | Appearance | Common In |
|---|---|---|
| Blade/ATO fuse | Flat, plastic with two metal prongs, colour-coded by amperage | Most Japanese imports (Corolla, Demio, Jazz) |
| Mini blade/ATC | Smaller version of blade fuse | Compact underdash applications |
| Maxi fuse | Large blade fuse, 20–100A | High-current circuits (underbonnet) |
| Fusible link | Thick wire or large flat link in underbonnet box | Main battery feed; not replaced like regular fuses |
| Glass tube | Cylindrical glass with metal end caps | Older vehicles; rare on post-2000 imports |
Fuse Amperage Colour Code (Blade Fuses)
| Colour | Amperage |
|---|---|
| Grey | 2A |
| Violet | 3A |
| Tan/Brown | 5A |
| Red | 10A |
| Blue | 15A |
| Yellow | 20A |
| White | 25A |
| Green | 30A |
Never replace a fuse with a higher amperage than specified. A 20A fuse in a 10A slot does not protect the wiring — it allows twice the rated current before blowing, potentially melting the wiring insulation.
How to Find and Check a Blown Fuse
Signs a Fuse Has Blown
- Something electrical has completely stopped working (interior lights, radio, power windows, horn, wipers, one set of headlights)
- Multiple related items stopped working simultaneously (e.g., all cigarette lighter sockets)
How to Check
Option 1: Visual inspection Pull the suspect fuse out (use the plastic fuse puller tool usually stored in the fuse box lid, or needle-nose pliers carefully). Hold it up to the light — you can see the metal strip inside. If the strip is broken or burned, the fuse has blown.
Option 2: Test light or multimeter With the circuit powered, touch a test light probe to each metal tab on the top of the fuse (without removing it). Both tabs should light the test light. If only one side lights, the fuse has blown.
Finding the Right Fuse
- Identify the circuit that has failed (e.g., the horn stopped working)
- Open the owner's manual and find the fuse diagram for your vehicle
- Find the fuse number listed for that circuit
- Locate that fuse number in the appropriate fuse box
- Pull and inspect
How to Replace a Blown Fuse
- Turn the ignition off before replacing any fuse
- Pull the blown fuse out with the fuse puller or pliers
- Insert a new fuse of the same amperage (same colour, same amperage number)
- Restore power and test the circuit
If the new fuse blows immediately or soon after: There is a short circuit in the wiring or a failed component drawing too much current. Simply replacing fuses repeatedly is not the fix — the underlying short circuit needs a mechanic's attention.
Fuses You Can Check Yourself (Common Culprits in NZ Cars)
| Problem | Check This Fuse Circuit |
|---|---|
| Interior lights not working | Interior lamps / room lamp fuse |
| Radio / infotainment off | Audio / ACC fuse |
| Power windows not working | Power window fuse (often separate per door) |
| Horn not working | Horn fuse |
| Wipers not working | Wiper fuse |
| Cigarette lighter / USB not working | Accessory / cigarette lighter fuse |
| One headlight out | Headlight fuse (per side or per beam) |
When to Call a Mechanic
- A fuse blows repeatedly — a persistent short circuit needs diagnosis
- You cannot identify which fuse has blown — a mechanic with a wiring diagram and test equipment can trace it quickly
- Main fuses or fusible links are involved — these protect the battery feed and require professional replacement
- Multiple systems have failed simultaneously — may indicate a wiring harness, ground, or module fault rather than a simple blown fuse
A basic fuse check and replacement is one of the cheapest electrical repairs possible. A mechanic will typically charge $80–$150 for diagnosis if you cannot identify the fuse yourself, and fuses themselves cost $1–$5 each.