How to Test an Alternator Without a Multimeter

By Jed Lehman •  Updated: 05/10/22 •  10 min read

In this article we show you how to test an alternator without a multimeter.

A faulty alternator is an automotive problem you’ll notice quickly. Alternator problems are detrimental because the alternator is responsible for supplying your vehicle with electricity. While a car’s battery is used to start the car and provide electricity when the engine is turned off, the alternator takes over this role when the engine is running. For this reason, a faulty alternator will prevent your car from starting and lead to other electrical problems.

One of the best ways to test an alternator is with a multimeter tool. However, sometimes you’ll find yourself with what might be an alternator issue and no multimeter. The good news is that we’re here to help. We’ll take you through several methods to test your alternator without a multimeter tool.

Skip ahead:

What Is an Alternator? 

How Long Do Alternators Last? 

Alternators on modern vehicles last for between 80,000 miles and 150,000 miles (on average). On older vehicles (before the 2000s) alternators last for about 50,000 to 100,000 miles; the older the vehicle the shorter the average alternator lifespan.

Given these mileage figures, the average modern alternator should last for between 6-12 years. The amount of years an alternator lasts depends on how many miles you put on the car and how often you start and stop the car.

Are Alternator Repairs Expensive?

Alternator repairs can cost upwards of $1,000 if it needs to be replaced. While some alternator repairs are expensive, minor repairs to belts and other alternator components can cost about $100 or $200.

Because there are a lot of factors at play when considering alternator repair costs you can expect to pay between about $250 and $750 when bringing your vehicle in for alternator problems.

Signs of a Bad Alternator 

Before you test your alternator it’s important to consider if you have an alternator issue or a different problem. We’re going to take you through a few signs of a bad alternator. If you’re experiencing any of the issues below we recommend testing your alternator.

Car Dies After Jump Start 

One of the most obvious signs of an alternator problem is your vehicle dying after a jump start. If the vehicle can be jumped and runs for a few moments before stalling, there’s a good chance it’s the alternator.

Another way to tell if it’s an alternator problem is to turn the car off and attempt to start it again after a jump start. Let the car run for about an hour before attempting this to allow ample time for the battery to charge. If you turn the vehicle off and it doesn’t start again, it’s likely the alternator because the battery was not charged.

Car Not Starting With New Battery 

A car that’s not starting can be caused by many things. It can be a fuse, a simple connection problem, or perhaps an issue with the starter. Issues with a car, not starting can also be caused by the battery or alternator.

The battery sends electricity to the starter to begin combustion and the alternator keeps the process going by keeping electricity stable. If your car is not starting because of battery problems or if your battery is dying frequently, your alternator can be on its way out. The alternator is also responsible for charging the car battery, so needing to frequently replace car batteries is almost always an alternator problem. 

Dimming Lights 

The alternator is responsible for sending electrical power through a vehicle when it’s running. When the alternator is working properly, the headlights are bright, the radio works well, and electrical functions are nominal.

If an alternator is no longer working properly or going bad, you’ll notice that headlights can get dimmer and even flicker. Lights inside the cabin and on the dashboard can also experience dimming and flickering. Some vehicles have indicators for an alternator that’s going bad but other vehicles don’t.

Indicator Lights and Other Electrical Problems

Some vehicles have indicator lights that alert drivers to alternator problems. On the dashboard, an alternator symbol will be displayed and it can be a static or flashing light. You can also look for other electrical problems aside from dimming lights. For example, slow-moving windows and an air conditioning that’s struggling are signs of a bad alternator.

How to Test an Alternator Without Using a Multimeter

Having a multimeter to test an alternator is one of the best ways to determine if it’s an alternator issue, battery issue, or something else. Luckily, you don’t need a multimeter to test the alternator if you don’t have access to one. Instead, there are several manual tests you can perform.

Accessory Test 

One of the best ways to test an alternator manually is with a simple accessory test. Alternators are responsible for sending power through a vehicle, so if accessories are not functioning properly there’s an issue with the alternator.

For an accessory test, we recommend checking as many accessories as possible. Doing so will give you an idea about whether or not a component is impacted by low electricity. The steps to perform an accessory test are listed below:

  1. Turn the ignition into the “on” position and start the engine. If the engine does not start you’ll want to move to a different test like the magnetic test.
  2. When the engine is running, start turning accessories on. Begin with the headlights.
  3. Then, move inside the cabin and turn on the radio and air conditioning.
  4. If turning on these accessories causes the engine to stall there’s an issue with the alternator.

The accessory test is always a good test to start with. It indicates that there’s a problem when the engine is running, which eliminates the battery as a potential problem.

Magnetic Test 

The alternator generates an electromagnetic field because of the rotor and stator. When an alternator is functioning properly the electromagnetic field is strong enough to attract some metal objects like wrenches, screwdrivers, and even screws.

On the other hand, if an alternator is not functioning properly it won’t have an electromagnetic field. You can test to see if an alternator has a magnetic pull with the steps below:

  1. Turn the ignition into the “on.” position without starting the engine
  2. Open the hood of your vehicle and locate the alternator.
  3. Hold a metal object that can be attracted to electromagnetic fields to the alternator (something like a wrench).
  4. If the object is pulled towards the alternator or sticks to the alternator the alternator is working. If there’s no magnetic pull, it’s not working.

You can also perform these steps with the engine running. We only recommend using this method because alternator problems commonly cause engine starting problems.

Sound Test 

The sound test is one of the simplest tests to perform on an alternator. When operating without issues, the alternator doesn’t make any noise. If there are issues with your vehicle’s alternator sometimes you can listen to the alternator and hear a squealing or growling sound. Performing the sound test is simple and the steps are listed below:

  1. Turn your vehicle’s ignition into the “on” position and attempt to start the vehicle.
  2. If the vehicle starts, open the hood and listen for any problems with the alternator.
  3. If the alternator doesn’t make a noise when the engine is running without accessories, begin to turn on accessories.
  4. With things like the air conditioning and headlights on, listen for noise again.
  5. The alternator will make a squealing sound if there are problems.

The sound test is tricky because the alternator doesn’t always make noise right away. In some cases, you might have to turn on several accessories before the alternator begins to struggle and squeal.

Battery Terminal Test

Another test you can perform is the battery terminal test. When an engine is running it doesn’t need the battery to send electricity to accessories or engine components. So, the thought here is that disconnecting the battery when the car is running should not affect the engine or vehicle’s accessories.

The battery terminal test is dangerous, though, because you can shock yourself when disconnecting the cables. Below are the steps to perform a battery terminal test in the safest way possible:

  1. Turn on the engine and let it run for a few moments.
  2. Open the hood and locate the battery.
  3. Wear protective gloves that shield you from electrical shocks.
  4. Locate the negative terminal and then remove the cable from the battery.
  5. Locate the positive terminal and remove the cable from the battery.
  6. Check on the engine and monitor how it runs.
  7. If the engine stalls or accessories begin to fail there’s an issue with the alternator.

We recommend against this test because it’s risky. You can get hurt because of the electricity, so always make sure you protect your hands and don’t touch anything that’s grounded in the engine bay.

Multimeter Test

If all else fails and you can’t tell if an alternator has a problem by manually testing it, it’s time to visit a technician or perform a multimeter test. You can find a multimeter online or at your local hardware store and they’re easy to use.

They come with a set of cables and indicate if an electrical component is generating electricity. Based on the design of the device, it will instantly show you if your alternator is faulty or broken.

You can also use a multimeter to test the battery and other components.

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To perform a multimeter test on an alternator the steps are listed below:

  1. Acquire a multimeter.
  2. Clean the alternator’s negative terminal.
  3. Set the multimeter to DC (voltage) and make sure the number is above 15.
  4. Place the multimeter’s negative cable on the terminal of the alternator (black cables).
  5. Obtain a reading and make sure it’s above 10 volts; an ideal reading for an alternator when the engine is off should be 12 volts.
  6. Then, start the engine.
  7. Again, check for a reading on the multimeter. This time, the reading should be between 14 and 15; the ideal range here is 14.2 to 14.8.
  8. Turn on engine accessories like the headlights, air conditioning, and radio.
  9. Take another reading of the multimeter. The reading shouldn’t fall below 12 volts, regardless of how many accessories you turn on.
  10. Turn off the engine and take one last reading. The multimeter should have a reading of at least 12.6. Anything less indicates a problem with the alternator.

Following these steps allows you to test your alternator with a multimeter. If any of the readings are off during the test, there’s an issue with the multimeter and you should take your vehicle to a professional technician. 

Wrapping Up 

Alternator problems are not uncommon because alternators don’t have the longest lifespan compared to other engine components. Still, alternator problems are easy to identify and test for because you’ll notice electrical problems with your vehicle.

If you perform the manual tests that we covered you’ll know if you have an alternator problem without having to use a multimeter or voltmeter tool. We always recommend checking again with a multimeter or taking your vehicle to a technician if you’re not sure about the problem.

Jed Lehman

Jed Lehman is a born gearhead who has been working on cars since he could crawl. He inherited his love for auto from his grandfather who owned a maintenance shop in Carlsbad, California. Jed is the driver behind Gearshift, and started this site to provide straightforward, helpful automobile information. From maintenance tips to product reviews, you can find it all here.