HomeTips & GuidesAlternator Wiring Connections: How To Wire An Alternator To Charge A Battery

Alternator Wiring Connections: How To Wire An Alternator To Charge A Battery

When it comes to automobiles, an alternator plays an important role as it powers the car’s electrical system and charges your battery when the engine is running. However, how does it work?  To learn more about alternator wiring connections, read the article below.

Table of Contents

How Does the Auto Alternator Work?

There’s a serpentine belt resting on a pulley attached to the alternator. Once you ignite the engine, the pulley rotates and moves the rotor shafts attached to your alternator. 

A rotor is an electromagnet with carbon brushes and two spinning slip rings attached to the shaft. As a result of the rotating, small amounts of electricity are supplied to your rotor and then conducted to your stator.

The magnets on your rotor are positioned in a way that allows them to pass over the copper wire loops in the stator. Therefore creating a magnetic field around the coils. Hence, the rotor spinning distributes the magnetic field, thus generating electricity.

However, the current generated is AC, which needs conversion to DC before use. Therefore, it’s channeled to the diode rectifier that converts the two-way current to a one-way flow direct current.

Then, the voltage passes to the voltage regulator, increasing or decreasing the voltage to meet your car’s system requirements.

After the electricity is sent to your battery and stored for future use, your engine powers your car’s electrical system if your engine is off.

However, if the engine is on, the alternator powers your car’s electrical system and charges your battery.

Auto Alternator Wiring Diagram: What Wires Go Where?

If you consider a standard GM alternator with an inbuilt regulator, most people refer to it as a three-wire alternator. However, in a real sense, only 2 wires are going in and out: the positive battery wire and the exciter wire.

The positive battery wire is larger in diameter and red in color. It either leads to your battery directly or via a wire junction from an output port on the backside of your alternator. 

Two wires opposite each other are referred to as terminal wires. 

One looped from your alternator’s terminal to the positive battery wire is the voltage sensing wire. It connects to the voltage regulator’s battery side, assisting the regulator to determine the voltage and regulate the output from your alternator.

The other wire connecting your alternator to the ignition switch is the exciter input wire. It connects to the ignition warning light, alerting the driver if the alternator isn’t malfunctioning. 

However, most people forget that there’s a fourth negative wire. It connects to your car’s chassis, providing a good connection for the sensor wire and helping reduce electric interference.

Vehicle Alternator Wiring

Caption: Vehicle Alternator Wiring

How to Wire an Alternator to Charge a Battery?

Wiring an alternator to charge your battery is relatively simple; all you need are the right tools and materials and some electrical circuit knowledge.

You’ll need the following tools.

First, ensure your alternator is functioning properly. A non-functioning alternator won’t be able to properly charge your battery.

Use your voltmeter to test the alternator. If the readings are more than 13V, then your alternator should be fine.

Checking your alternator with a voltmeter

Checking your alternator with a voltmeter

Now, you can begin wiring your alternator to charge your battery.

  • Begin by connecting the alternator’s battery positive wire to the positive terminal on your battery.
  • Continue to connect the alternator’s negative terminal to the car’s chassis.
  • Then, use cables or wiring harnesses to connect the alternator’s remaining terminals to the battery’s corresponding terminals.
  • Finally, start your engine and keep it on for a few minutes to allow the alternator to begin charging your battery.

You can use your voltmeter to confirm your battery’s voltage (it should be 12.6V or more). If the voltage is lower, your alternator or battery could be faulty, and you’ll need professional assistance. 

Custom Wiring Harnesses or Cables at Cloom

The connection between all the wires ensures your alternator functions properly, charging the battery and powering your car’s electrical system. For an easy installation, you may need a custom wiring harness.


Alternator wires are in charge of transferring electricity from your alternator to your battery. The wires are normally made of aluminum or copper and are covered in protective insulation to prevent shorting out.

Wire thickness is also important. If the wire is too thin, it might overheat, and the wire will be difficult to route through your engine bay. When deciding on the wire thickness, take the wires’ length and the load’s amperage.

Generally, alternator wires are available in sizes such as 14 gauge, 12 gauge and 10 gauge.


Alternator wires are usually red in color. You need to connect the red wire to the positive terminal of your battery. Then, attach the negative wire, commonly black, to a metal surface on your car, such as the frame or a bolt.

In some cases, vehicles may have alternator wires that come in colors like blue or green. These colors typically indicate that the wire is carrying a higher voltage. If you’re unsure about the wire, refer to your car’s manual or seek advice from a mechanic.


Typically, alternator wires have two types of terminals: ring terminals and spade terminals. The ring terminal connects the wire to the battery, while the spade terminal connects it to the alternator.

Make sure you use the right size when connecting wires to these terminals. Using a size that’s too small might cause the terminal not to fit while using a size that’s too big might result in a loose connection. 

Alternator attached with wiring harnesses.

Alternator attached with wiring harnesses.


That covers everything you need to know about wiring an alternator for your car. For all your alternator-related plug-and-play wiring harnesses, feel free to contact Cloom Tech.

Hi I am Christa, sales manager of Cloom.

I have extensive expertise and experience in wiring harnesses and I believe I can help you.

And we have a very professional technical team who can clearly understand the customer’s needs and give professional suggestions and solutions after receiving the drawings.

If you also have wiring harness needs, please send me the drawing so that we can give you our quote and start our business.

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