Fuses and Relays
Fuses protect electrical circuits by failing deliberately when current exceeds a safe level. Relays let a small switch control a high-current circuit such as a fuel pump or headlights.
What it does
A fuse contains a thin element that melts and breaks the circuit under excessive current, protecting the wiring from overheating. A relay uses a low-current coil to close a set of high-current contacts.
Signs a fuse or relay is failing
- A single electrical component that has stopped working entirely
- A fuse that blows again immediately after replacement, indicating a short
- A clicking from the relay box with no result
- Intermittent operation of a circuit, often a failing relay
When to replace them
Not scheduled. Replaced when they fail. A fuse that blows repeatedly is reporting a fault elsewhere and should not simply be uprated.
What to confirm before ordering
Have these ready and the counter can usually confirm the part in under a minute.
- Correct amperage rating, which must never be increased
- Physical fuse type, whether standard, mini or cartridge
- Relay pin configuration and coil voltage
- Whether the circuit has been checked for a short before refitting
Fuses and Relays questions
Why does my fuse keep blowing?
A repeatedly blowing fuse is reporting a short or an overload in the circuit it protects. Fitting a higher-rated fuse removes the protection and puts the wiring at risk of a fire. Find the fault instead.
Can I fit a higher amperage fuse?
No. The rating is chosen to protect the wiring in that circuit. A higher-rated fuse lets the wiring, rather than the fuse, become the weakest point.