How To Use a Multimeter On a Car
Author: Toby Date Posted:25 July 2025
Whether you're diagnosing a dodgy battery, checking a fuse, or testing your alternator, a multimeter is one of the handiest tools in any DIY mechanic’s kit. If you’ve never used one before, don’t stress — it’s easier than you think, and can save you a tonne on basic diagnostics.
Let’s break it down into simple steps so you can start troubleshooting like a pro.
What Is a Multimeter?
A multimeter (or multi-tester) is a compact device used to measure key electrical values like voltage (V), current (A), and resistance (Ω). For automotive use, it’s one of the most essential tools in your kit — especially when you’re trying to figure out why your car won’t start, if your battery’s on its last legs, or if a fuse has blown.
Here’s what it’s commonly used for:
- Measure battery voltage – helps you know if your battery needs recharging or replacing
- Check alternator output – to make sure your charging system is working properly
- Test fuses and relays – for quick diagnosis of blown components
- Trace wiring faults – especially handy for older vehicles or aftermarket installs
There are analogue types, but digital multimeters (DMMs) are now the go-to — they’re more accurate, easier to read, and safer for everyday use. Whether you're diagnosing a flat battery or double-checking a dodgy connection, a multimeter can point you in the right direction fast.
Understanding the Multimeter Settings
Most digital multimeters come with a rotary dial. Here’s what the main settings usually mean:
| Symbol | Function | When to Use It |
|---|---|---|
| V (with a straight line) | DC Voltage | Car batteries, sensors, wiring |
| V (with a wavy line) | AC Voltage | Household current — not usually used for cars |
| Ω (ohm symbol) | Resistance | Testing continuity or resistance in a wire/component |
| A or mA | Current | Testing amps — not commonly needed unless advanced testing |
| Continuity (sound wave symbol) | Circuit continuity | Fast way to check if a circuit is complete |
Basic Multimeter Tests Every Driver Should Know
1. Testing Your Car Battery
Start by setting your multimeter to DC Voltage — ideally the 20V range. With the engine off, touch the black probe to the negative terminal and the red probe to the positive. A fully charged, healthy battery should show around 12.6 volts.
Now start the engine and check again. The reading should climb to somewhere between 13.7V and 14.7V, which means the alternator is doing its job. If you’re seeing anything below 12V, your battery might be weak or on its way out.
2. Checking a Fuse
Set your multimeter to Continuity or Resistance (Ω) mode. Remove the suspect fuse from its housing, then touch a probe to each end.
If the multimeter beeps or shows 0 resistance, the fuse is still good. But if there’s no sound or the screen shows infinite resistance, you’re looking at a blown fuse that needs replacing.
3. Testing the Alternator
To check your alternator’s health, leave the multimeter on DC Voltage. With the engine idling, take another voltage reading at the battery terminals.
A good alternator should show a steady charge between 13.7V and 14.7V. Anything lower means it might not be charging properly, while anything above that range could point to an overcharging issue — both worth getting checked out.
Tips for Safe Use
- Always start with the correct setting — using the wrong one can damage the multimeter or give false readings.
- Insert probes firmly into ports and make sure your fingers don’t touch exposed metal tips.
- For current testing (amps), never use this on a car battery unless you're confident — it requires breaking the circuit.
A Handy Tool for Any Driveway Mechanic
Whether you're chasing down an electrical gremlin or just checking if your battery’s still got life, knowing how to use a multimeter is a valuable skill. It gives you insight into your vehicle’s electrical system without needing a trip to the shop every time something flickers or fails.
Looking to grab one for yourself? At Superspares, your trusted auto parts online shop, we stock a range of quality multimeters and vehicle diagnostic tools — delivered fast and backed by expert service.
Explore our range online and level up your DIY game today.
