Updated at: 17-08-2022 - By: Lucas

Since we’ve written about alternators extensively, we’ve covered everything from diagnosing alternator problems to selecting the best replacement and describing how you can put one in your vehicle on your own.

You asked for it, therefore we answered it here so you can go out and rewire your car with a 3-wire alternator even if it isn’t an option from the factory!

How to Connect a 3 Wire Alternator

3 Wire Alternator Wiring Diagram-2

An alternator converts mechanical energy generated by the spinning of the engine and movement of the drive belt into electrical energy. When the engine is operating, the alternator serves as the primary source of power for both the battery and the rest of the car.

The name “3 wire alternator” comes from the fact that it uses three wires to operate. When replacing an alternator directly, the procedure is as simple as remembering where the plugs are located, removing them, and then reinstalling the new alternator.

If you need detailed instructions on how to remove an old alternator and replace it with a new one, see our previous article on alternator repair.

  • Identify the three connection points on the alternator. The bottom connection is a bolt for the o-ring wire connector to sit on. On the top, terminal 1 and terminal 2 are positioned next to each other and accept small plugs.
  • Place the o-ring of the positive battery wire on the bolt. Every car should have one by default regardless of the alternator type.
  • Get a short piece of wire with an adequate terminal plug on one end, and an o-ring on the other. Plug the wire into terminal 2, and place the o-ring side over the bolt, after the red wire. 
  • Tighten the bolt with a nut to connect the two o-rings with the alternator.
  • Terminal 1 should be connected to the gen, battery, or alt dashboard light. On the cars that don’t have it, you’ll wire a dummy light between terminal 1 and the On position of the ignition switch.

You’ll need to follow these instructions if you want to connect a 3-wire alternator without using a reference or appropriate plugs:

Now, let’s go over what each step accomplishes. Making sure they aren’t mistaken is critical when doing the identification process.

The red wire with an o ring is the positive lead. It transmits electricity to the battery, whether or not it passes via a junction block (a cable intersection).

Terminal 2 is connected to the positive lead and produces a tiny circuit. No idea what it does, but you can verify the terminal’s 1 letter code online.

A dashboard light, a diode, or an LED is connected to Terminal 1. Due to its lack of lighting, it’s commonly referred to as the “dummy light.” The diode is connected to the ignition switch’s On position by a wire.

It’s called a “excited alternator field” because the diode lights up when the ignition is turned on. Flipping it back on will stop the diode from draining battery juice.

As soon as the key is released, the alternator will begin to run and can be switched off by the key being shifted to off position. The diode prohibits two-way current flow.

3 Wire Alternator Wiring Diagram


Why does the alternator have 3 wires?

3 wire alternator senses voltage at the fuse box and ignition to regulate and modify the charge. Alternators with 2 or more wires can be retrofitted into earlier cars using the instructions provided in the preceding section.

What are the three wires for my alternator?

There are two sets of wires: one that goes directly to the battery and one that connects to the battery via a wire junction.

The second and third wires are termed terminal wires because they are located next to each other. The voltage detecting wire is connected to terminal 2, whereas the exciter/ignition input wire is connected to terminal 1.

What is a 3 pin alternator?

We have been discussing the 3 wire alternator, also known as the 3 pin alternator, throughout this post. It’s a 3 pin alternator, however the positive battery cable is screwed into the alternator wire post rather than hooked in.

What brand of the alternator is the best?

Because of their low cost, high quality, and wide availability, we believe ACDelco alternators are the best on the market. Take a look at our most recent article on the top 6 alternator choices if you’re interested in learning about some of the other excellent choices.

How many wires go to an alternator?

The exciter wire and the positive battery wire are both connected to the 3 wire alternator. The alternator’s terminal 2 is connected to the alternator’s positive battery wire post via a sensing wire.

Can I run a wire from the alternator to the battery?

While the battery is being recharged, you should connect the positive battery wire from the alternator to the battery so that the alternator can power both the battery and the engine.

What happens when the alternator goes bad?

The car won’t be able to run for very long if the alternator fails. Alternators are critical components of the vehicle’s electrical system, and one that is malfunctioning will render the vehicle inoperable.

Without it, the automobile can only run for an hour or so on the electricity stored in the battery.

What is the small wire on an alternator?

The alternator’s output is determined by the sensing wire, a thin wire that loops from one component of the alternator to another. For the electrical systems and engine to function properly, this is a crucial component.

How do you manually excite an alternator?

Alternatively, if you don’t have the exciter wire, you can run a short wire from R to the battery wire terminal. Remove the component as quickly as possible to avoid heating up the wire from the current and avoid touching the exposed areas of the wire.

Where does the alternator exciter wire go?

While the starter turns the engine, the exciter wire should be connected to the ignition to energize the alternator field. Exciting wires are no longer in use, with the positive battery terminal taking over and the sensor wire taking over.

Does the alternator need a ground wire?

Because the alternator is grounded to the engine block, it does not require a ground wire.

Are 13.8 volts good for alternators?

The alternator needs at least 13.8 volts to recharge the battery and power the system, but that’s only on the cusp of what’s considered the absolute minimum.

Keep an eye on your battery voltage when charging to ensure that it doesn’t fall below 13. 8 volts, or you could run out of power while driving.

Why is the alternator connected to the engine?

The alternator and starter are either linked directly, via a wire junction, or not at all… I’m not sure why this is, but the two modules don’t interact in any way, shape, or form.

There is a starter and an alternator in a car, both of which use battery power to start and charge the vehicle’s electrical systems and batteries.

Are 14.8 volts too high for an alternator?

14 volts is OK, with 14. 6 to 14. 7 volts as the upper limit. Please refer to our discussion about alternator overcharging to ensure that yours is in good working order..


3 wire alternators are basic, but if you’re not careful, you could end up with major electrical problems.

I recommend working with a friend to ensure that all of the wires are connected properly. You don’t have to be an expert to complete the task; all you have to do is route the wires appropriately!