Emergency & Roadside

The Small Electrical Kit an Older Car Should Carry

A blade-fuse assortment and a tester turn a dead circuit at the roadside into a two-minute fix — as long as you obey the one rule that stops it starting a fire.

By Antoni DaskalskiPublished 1 August 20263 min read

A blown fuse is one of the few roadside electrical faults an ordinary owner can actually fix, and the kit to fix it is tiny and cheap. An assortment of blade fuses and a tester lives in the glovebox and turns a dead circuit — no lights, no fuel pump, no wipers — into a two-minute job.

There is one rule that matters more than the kit, and getting it wrong is genuinely dangerous. So this guide is mostly about that rule.

The rule: never go up a rating

The fuse is meant to be the weakest point in the circuit. It is sized to fail before the wiring does, so that a fault blows a cheap replaceable component instead of melting the harness behind the dash.

Fit a fuse rated higher than the one that blew and you have defeated that entirely. More current now flows before anything gives way, and the thing that gives way is the wire, which is a fire in a place you cannot reach while driving. This is the mistake the roadside kit exists to prevent, not enable: replace like for like — the same amperage and the same physical type — every time.

What the kit needs to contain

A range of amperages, in the right physical types. Cars mix fuse form factors, so carrying only one size is how you end up unable to fit anything. The common blade types are:

Standard (ATO / ATC): About 19 mm — the classic blade fuse
Mini (ATM / APM): About 11 mm — common on newer circuits
Maxi (APX): About 29 mm — high-current circuits
Colour coding: Amperage by colour, per the ISO 8820 standard

Match the blown fuse on both amperage and size. The colour and the number on top both give the rating, so a spare of the right colour is usually the right amperage — but read the number too, since a faded fuse can mislead on colour alone.

A tester or puller. A blown fuse can look perfectly intact; the element cracks in a way that is hard to see. A cheap fuse tester or test light finds the dead one without pulling and squinting at every fuse in the box, which on an older car with the panel tucked behind a kick panel is most of the job.

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Automotive fuse assortment and tester

An assortment covering the amperages and physical sizes your car uses, plus a tester. Match the blown fuse on both.

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Where it lives, and what it sits beside

In the car. The glovebox or a boot organiser, alongside the rest of what an older car should carry — which, ordered by how likely each failure actually is, is in the roadside kit for a car that might not start. The visibility gear that keeps you safe while you swap a fuse on a verge is in the roadside visibility kit.

The one tool that turns "the fuse keeps blowing" from a mystery into a diagnosis is the multimeter — a multimeter for car owners, not electricians covers the fuse and continuity checks that find the fault behind a dead circuit.

Questions people actually ask

What is the one rule I must not break?

Never fit a fuse rated higher than the one that blew. The fuse is deliberately the weakest point in the circuit, sized to fail before the wiring does. Fit a higher rating and you have removed that protection — the next fault melts the harness instead of popping a fuse, and that is a fire. Always replace like for like, both the amperage and the physical type.

The new fuse blew straight away. Now what?

Stop replacing it. A fuse that blows again immediately is not a bad fuse — it is telling you there is a fault downstream: a short, an overload, or corrosion. Swapping in fuse after fuse just burns through your kit while the real problem sits there. That is the point to reach for a multimeter and find the short rather than feed it.

How do I know which fuse type my car takes?

Look at the ones already fitted, and carry a range. The common blade types are Standard (ATO/ATC, about 19 mm), Mini (ATM/APM, about 11 mm) and Maxi (about 29 mm, for high-current circuits), and a car often uses more than one. A good assortment covers the amperages and the physical sizes, so match both against the blown one rather than forcing a fuse that nearly fits.

What does the fuse colour tell me?

The amperage. Blade fuses are colour-coded to a standard — the colour and the number printed on top both give the rating — so a spare of the right colour is a spare of the right amperage. It is a quick visual check, but read the number too, because a dirty or faded fuse can mislead on colour alone.

Do I need the tester, or just the fuses?

The tester earns its place. A fuse can look intact and be blown — the element cracks in a way that is hard to see by eye — so a cheap fuse tester or test light tells you which one has gone without pulling and squinting at every fuse in the box. On an older car with an awkwardly placed fuse panel, that is the difference between a two-minute job and a roadside puzzle.

Where should this kit live?

In the car, not the garage — a fuse kit at home does nothing for a dead circuit fifty miles away. The glovebox or a boot organiser is the right home, alongside the rest of the roadside kit. It is small, cheap and one of the few spares that turns a stranding into an inconvenience.