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How to Check Alternator Amperage With Multimeter? Guide 2023

The alternator in your vehicle is a silent hero, quietly powering all your electrical systems, from the headlights to the radio to keep you occupied on the road. A crucial aspect of keeping your vehicle running smoothly is ensuring that the alternator is performing optimally, which involves checking its amperage output. Knowing how to check alternator amperage with multimeter is cost saving skill. You can use this process to diagnose alternator problems before alternator leave you stranded. 

What Is an Alternator?

An alternator is an essential part of your vehicle's electrical system. Your car's alternator generates electrical power in the form of alternating current (AC), which is converted into direct current (DC) to charge the battery and power various electrical components.

What Is an Alternator

Imagine it as your car's electricity generator. Testing alternator amperage requires an understanding of how it works. If you don't have multimeter then you can take our guide on How To Check Alternator Without Multimeter?

Why Test Alternator Amp Output?

Testing your alternator's amperage output is essential since it directly affects your vehicle's performance. From your headlights to your radio to your engine control unit, your alternator ensures that your car's battery remains charged. An alternator that isn't working properly can lead to a drained battery, which can leave you stranded.

In addition, a malfunctioning alternator can cause electrical problems, poor fuel efficiency, and even engine failure. In order to maintain the reliability and performance of your vehicle, you must understand the importance of testing alternator amperage.

Can You Really Check Alternator Amperage with a Multimeter?

Yes, you can use a multimeter to check your alternator's amperage. This task could be easily accomplished with the help of a multimeter, a versatile tool that measures electrical current, among other things. If you understand how your alternator works and how multimeters work, you'll be capable of performing this test and gain valuable insight into the electrical health of your vehicle. 

How to check alternator amperage with multimeter| Step By Step Guide

This section will show you how to test your alternator amperage using a multimeter step-by-step. To ensure an accurate assessment of your vehicle's electrical system, follow these simple instructions.

Step 1: Safety Precautions

How to check alternator amperage with multimeter

It is essential to prioritize safety before you begin. Park the vehicle on a level surface and turn off the engine. To prevent an unexpected movement of the vehicle, engage the handbrake. When working with electrical components, wear safety goggles and gloves to avoid any potential accidents.

Step 2: Preparing Your Vehicle

How to check alternator amperage with multimeter

Prepare your vehicle for the amperage test by popping the hood and locating the battery and alternator. It should be easy to access the battery. If you are unsure of the locations, consult your vehicle's owner's manual. Get to know the positive and negative terminals of the battery and the housing of the alternator.

Step 3: Accessing the Alternator

How to find alternator in car

An alternator is typically connected to the engine by belts. Typically, it's a cylindrical or rectangular component with a pulley at the front. Identify the output terminal on the alternator's housing, where you will connect your multimeter.

Step 4: Testing Amps

Set your multimeter to measure DC amperage within the appropriate range. Don't forget to check the polarity of the multimeter's leads; the positive lead should be connected to the positive terminal and the negative lead to the negative terminal. Start your vehicle and let it idle for a few minutes.

How to attach multimeter probe to alternator

Check the multimeter's reading, which should show the alternator's amperage output. There are a wide range of alternator ratings on late-model vehicles, ranging from 60 to 150 amps. Alternators with high output can generate up to 200 amps. Alternators are matched to vehicles' electrical systems based on their amp ratings.

Step 5: Inspecting the Battery

How to check car battery with multimeter

It is a good practice to monitor the battery's voltage while testing the amperage. Check the battery's voltage with your multimeter. Set the mutlimeter on DC voltage and attach positive lead to postive teminal of battery and negative lead to negative terminal. Typically, a healthy battery should register between 12.6 and 12.8 volts. It may indicate a battery issue if the voltage is significantly lower.

Step 6: Examining the Alternator Voltage

You should also measure the alternator's voltage output in addition to its amperage. Set the multimeter to DC voltage and connect the multimete probes. Positive probe will be connected to positive terminal and negative probe will be connected to negative terminal.

How to check alternator voltage

The multimeter should be connected to the alternator's output terminal. If the alternator is working properly, you should see a voltage reading of 13.8 to 14.4 volts when the engine is running. Alternator problems may be indicated by voltages outside this range.

Step 7: Locating the Power Amp Output Wire

How to check alternator output wire

Identify the power amp output wire on the alternator to complete the test. Electrical power is delivered to the battery and other vehicle systems through this wire. Secure it and make sure it is not damaged or corroded.

Step 8: Setting the Multimeter to Read Amps

Don't forget to return your multimeter to its default settings before you finish the test. Disconnect the leads, turn off the engine, and store your testing equipment safely. Close the hood of the vehicle and secure the alternator housing.

Can a bad alternator drain a battery?

It is true that a bad alternator can drain a battery. During engine operation, the alternator recharges the battery. If it fails, the battery's power is used to power the vehicle's electrical components, causing it to gradually lose charge.

Can a bad alternator drain a battery

As a result, your battery may eventually die, leaving you stranded. The battery weakens over time, resulting in difficulty starting the vehicle. Maintaining your vehicle's overall electrical system and preventing battery problems depends on a working alternator.

How do I know if I need a new alternator?

Is your vehicle showing signs of alternator failure? Check out these common indicators to see if it's time for a replacement. Knowing how to check alternator amperage with multimeter is easier when you notice the bad symptoms of alternators.

1. Dimming Headlights and Dashboard Lights

Your dashboard and headlights may appear dimmer when you're idling or driving at low speeds, which could indicate an alternator problem. Electrical power may not be sufficient to maintain proper lighting if an alternator is weak.

2. Warning Lights on the Dashboard

How do I know if I need a new alternator

The warning lights on modern vehicles illuminate when something goes wrong. It is a clear sign that your alternator is malfunctioning if your battery or alternator warning light remains lit. Make sure you don't ignore it.

3. Strange Noises

Keep an eye out for unusual noises coming from the engine compartment. Grinding, whining, and squealing sounds can be produced by a failing alternator. Wear-out bearings or a damaged belt can cause these noises, indicating a problem with the alternator.

4. Difficulty Starting the Engine

It is possible for your vehicle's battery to become uncharged if the alternator is weak or failing. Your alternator may not be properly recharging your battery if you are having difficulty starting your car or need to jump-start it frequently.

5. Electrical Issues

You may experience erroneous behavior from a variety of electrical components when your alternator malfunctions. A malfunctioning power window, radio, or air conditioner are examples of these issues. Electrical performance that is inconsistent is a red flag for alternator problems.

6. Battery Problems

There are several causes of battery problems, but they are often linked to alternator issues. Your alternator's inability to replenish your battery's charge may be the root cause of your battery constantly running low, despite recharging or replacing it.

7. Stalling or Unpredictable Engine Behavior

Having a struggling alternator can affect the performance of your engine. The car may stall, surge, or idle erratically as a result. Consider having your alternator checked if your vehicle's engine behaves unpredictably.

8. Burning Smell

You may detect a burning odor coming from your engine if your alternator is failing. A burnt smell can be produced when insulation on the alternator's wiring melts due to excessive electrical load.

How long will a car run with a bad alternator?

A car without a functioning battery won't run for more than 10-20 minutes with a bad alternator. When the alternator fails to charge the battery, the car will stall. It generally runs for a few minutes, not hours, depending on the state of the battery and the vehicle's power consumption. Avoid getting stranded on the road by addressing alternator problems promptly.


First you should know the working of alternator and sign of fall alternator then you processed further for testing. I recommend you to take action immediately if you notice any bad sign of alternator. When you begin for testing the alternator, you need to take safety first. Now I hope you know very well How to check alternator amperage with multimeter.  

Best of Luck