How To Test Alternator With A Multimeter (9 Step Guide)

Want to learn how to test alternator with a multimeter?  Super stuff, you are in the right place!

In this ToolGaloreHQ.com blog, we will show you:

  • How to diagnose your alternator;
  • Typical loads that are affected;
  • Step by step testing procedure; and
  • So Much More!
How to test alternator with a multimeter

Why This Guide On How To Test Alternator With A Multimeter

If you're experiencing problems with your car, such as it not starting, or if it's jerking and hesitating while you're driving, then it might be a good idea to test the alternator. The alternator is responsible for charging the battery and providing power to the car's electrical systems (amp loads). 

alternator loads in a car
Keep in mind that there are a few things that you can do to troubleshoot an alternator that's not charging correctly, such as checking the fuses, wiring, and belt for damage or wear. 


With a little bit of time and effort, you should be able to diagnose and fix the problem quickly and easily.


Most alternators are rated and capable of providing 65 to 100 amps, which is capable of handling the car's electrical requirements from the headlamps, the internal circuitry, the aircon system and fuel pumps.

Fortunately, testing the alternator is a relatively simple process and this can be done with a multimeter. In this article, we'll show you how to do it.

Common problems faced with alternators

The most common problem that people face when testing the alternator with a multimeter is not being able to find the right terminals.

In most cars, the alternator is located near the battery, and it's usually pretty easy to spot. However, the terminals can be a little tricky to find. They're usually hidden behind a plastic cover, and they might be labeled something like "BAT" or "ALT."

Another common problem is not being able to get a good reading on the multimeter. This can be caused by a variety of factors, including a bad connection, a faulty multimeter, or an overloaded electrical system.

Finally with all the common problems above, it's important to note that testing the alternator should not be used as a diagnostic tool for determining whether or not your car has a problem.

The only way to accurately diagnose an alternator problem is to take the car to a mechanic. Do not try and fix a problem you are not qualified or comfortable with fixing. 

Read More:>>> Learn How To Test Car Battery With A Multimeter

What You Need To Know About How To Test Alternator With A Multimeter

When testing the alternator with a multimeter, you're looking for two things: the voltage output and the amperage output.

The voltage output should be between 13.5 and 14.5 volts. If it's lower than that, then the alternator isn't charging the battery correctly. The amperage output should be between 30 and 40 amps. If it's lower than that, then the alternator might be having trouble providing power to the car's electrical systems.

how to test alternator


It's important to note that these are just ballpark figures. Every car is different, so you might need to adjust the numbers a bit depending on your vehicle. Be sure to check your specific car's user manual for the exact specifications of the alternator installed.

What To Look Out For When Learning How To Test Alternator With A Multimeter

Common Issues and problems

Below are a couple of common problems and potential telltale signs that your alternator may not be functioning correctly.

1. The alternator isn't charging the battery correctly.

One common problem with alternators is that they might not charge the battery correctly. This means that the car might not start or it might jerk and hesitate while you're driving. You can test whether or not your alternator is working properly by using a multimeter.

2. The alternator isn't providing power to the car's electrical systems correctly.

If the amperage output is lower than it should be, then the alternator might not be providing power to the car's electrical systems correctly. This can cause a variety of problems, such as the car not starting or the headlights not working properly.

Read More:>>> Test a 3 Wire Crank Sensor With A Multimeter

3. The alternator is making noise.

If the alternator is making noise, then it might be indicative of a problem. Alternators shouldn't make any noise when they're working properly. If you hear a whining or grinding noise, then it's likely that the bearings are going bad and the alternator will need to be replaced.

4. The alternator is putting too much strain on the battery, which can lead to battery failure.

If the alternator is putting too much strain on the battery, then it can lead to battery failure. This usually happens because the alternator is working overtime to try and charge a dead or dying battery.

As mentioned above, if these issues persist and are clearly experienced, then take the car in to a mechanic for a thorough assessment.


Equipment You'll Need To Effectively Learn How To Test Alternator With A Multimeter

In order to test the alternator with a multimeter, you'll need a few basic pieces of equipment. These include:

  • Multimeter,
  • Set of jumper cables, and
  • Battery charger.

Step by Step Guide On How To Test Alternator With A Multimeter

Step 1

Park the car on a level surface and turn off the engine.

Step 2

Open the hood and disconnect the battery cables.

Step 3

Attach one end of the jumper cables to the positive terminal of the battery.

Step 4

Attach the other end of the jumper cables to the positive terminal of the alternator.

Step 5

Connect the negative terminal of the jumper cables to a piece of metal on the car's chassis (not on the battery).

Step 6

Turn on the ignition and let the engine run for a few minutes.

Step 7

Take a reading on the multimeter. The voltage output should be between 13.5 and 14.5 volts. If it's lower than that, then the alternator isn't charging correctly.

The amperage output should be between 30 and 40 amps (Or whatever your car's rated capacity provides). If it's lower than that, then the alternator might be having trouble providing power to the car's electrical systems.

Step 8

If the multimeter readings are outside of the acceptable range, then further diagnosis will be needed to figure the problem.

Step 9

Once you're done testing, turn off the engine and disconnect the jumper cables.

Tips to Diagnose Alternator

There are a few things that you can do to troubleshoot an alternator that's not charging the battery or providing power to the car's electrical systems correctly. This includes:

  • Checking the fuses and wiring for any damage or corrosion.
  • Monitoring the voltage at the battery. If it's below 12 volts, then the alternator might not be charging the battery correctly.
  • Inspecting the belt for signs of wear or damage.
  • Performing a visual inspection of the pulleys for signs of wear or damage.
  • Replacing the spark plugs and air filter, as this can help improve the performance of the alternator.

Read More:>>> Find Top of the top HVAC Multimeters

Final Thoughts on How To Test Alternator With A Multimeter

Testing the alternator with a multimeter is a simple process that can help you determine if there's a problem with your car's charging system.

By following the steps in this guide, you'll be able to test the voltage and amperage output of your alternator quickly and easily. If the readings are outside of the acceptable range, then further diagnosis will be needed to figure out what the problem is.


Mogale Modisane

Mogale Modisane

Mogale is a qualified B(Eng): Electrical Engineer. With experience working on large-scale Solar, Wind, and Hybrid Projects. He has been exposed to multiple tools throughout his career and has a keen interest in breaking down the often murky world of power tools, machines, and measurement equipment making them more accessible and understandable to everyone.

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Mogale Modisane

Mogale Modisane

Mogale is a qualified B(Eng): Electrical Engineer. With experience working on large-scale Solar, Wind, and Hybrid Projects. He has been exposed to multiple tools throughout his career and has a keen interest in breaking down the often murky world of power tools, machines, and measurement equipment making them more accessible and understandable to everyone.

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