HomeTips & GuidesOne Wire Alternator Wiring: How To Wire Alternators in Old or Classic Cars

One Wire Alternator Wiring: How To Wire Alternators in Old or Classic Cars

What is one-wire alternator wiring? Compared to their three-wire alternator counterparts, 1-wire alternators are affordable, compact, and easy to wire. 

So most classic, street rod, classic muscle, and custom car builders use them to keep the engine bay clean and uncluttered. 

These power sources are also ideal for converting old vehicles from generating six volts to 12 volts. 

So let’s look at the one-wire alternator wiring to see how to fit one into your car.

Table of Contents

What Is an Alternator?

An alternator is an electric power generator that converts mechanical energy to AC in vehicle engines. 

The AC then gets converted to DC to charge the battery. Batteries power all car components using DC energy when the engine is off, but the car alternator handles most of the load when the engine is running.

How Alternators Work

Alternators have four primary components that enable them to supply your vehicle’s electric demands and run efficiently.

Rotor and Stator

The rotor is a cylindrical component surrounded by magnets. On the other hand, a stator is a wiring set fixed on the alternator housing.

 Rotors spin inside the stator to create alternating magnetic fields that induce alternating current in the coil windings.

Voltage Regulator

This component keeps tabs on the voltage generated by the alternator. 

Since the power output from the mini generator varies depending on the engine RPM, it can overpower or underpower car components.

Voltage regulators monitor the voltage output to make the necessary adjustments by playing around with the duty cycle or the electric field.

The internal structure of a car alternator

The internal structure of a car alternator

If the engine is revving at slow speeds and the output is low, the regulator switches current on from the rotor for extended periods and off for short periods. 

And if the power generated is high, it switches the AC on for short lengths and off for extended periods. 

These adjustments keep the supply almost constant at all times.

The technical explanation behind this operation can be complex because it involves adjusting the alternator’s field circuit.

In most cars, the voltage generated by the alternator must be higher than the car battery because it must charge the battery, then send the rest of the power to run other components. 

So this regulator must perform a delicate load-balancing act at all times.

Diode Rectifier

Diode rectifiers convert AC to DC to charge the battery and power the different car systems.

A rectifier for a car alternator

A rectifier for a car alternator

Cooling Fan

Alternators generate heat when running, and the fan keeps the internal parts cool for efficient power generation.

One Wire Alternator Wiring Diagram

1-wire alternators have a self-exciting internal voltage regulator. So you don’t need to run an additional wire to the external voltage regulator to complete the ignition turn-on loop circuit.

A car alternator to battery wiring diagram

A car alternator to battery wiring diagram

The device only needs one wire to connect to the battery, which makes its wiring simpler and installation easier. But it has some drawbacks.

But before discussing these disadvantages, let’s look at the 3-wire alternator.

What Are Three Wire Alternators?

Also known as 3-pin alternators, 3-wire alternators feature external voltage regulators and three electrical pins.

  • Output/charge wire (the red wire that connects to the battery’s positive terminal)
  • Field wire (provides the alternator with the required magnetic field to generate electricity)
  • Sense wire (provides voltage feedback to the external regulator to ensure the charging voltage is constant)

Although this type of alternator requires more wiring, it is more intelligent because it has a better sense of the electrical current load.

 The sense wire provides feedback from the fuse box and ignition to ensure the mini generator provides enough electricity even at low engine RPMs.

1-Wire vs. 3-Wire Alternator Wiring Diagrams

The single vs. three-wire difference introduces other variations between these two alternators.

For starters, the self-exciting regulator design of the 1-wire alternator means it has to get to a certain rotor spinning speed to charge the battery. 

So you must rev the engine to increase the alternator RPM to a certain level to begin charging.

A classic car engine with an alternator connected to the engine via a belt

A classic car engine with an alternator connected to the engine via a belt

Therefore, idling the engine for long periods can drain the battery because the alternator might not charge or will produce insufficient current to charge the battery.

Also, this alternator only has a sense of what it sends the power to, the battery. 

So if the battery is good and fully charged, it won’t notice voltage drops when the electrical demand increases.

But 3-wire alternators are more up to the task because they can adjust their output to match the demand. 

And you don’t have to worry about power requirements even at low RPMs when idling the engine.

A three-wire alternator

A three-wire alternator

For instance, if your car has a sophisticated fuel injection system that adjusts starter parameters, a one-wire unit might not be sufficient to keep up. But the three-wire unit alternator works just fine.

One Wire Alternator Wiring Steps

Typical one-wire alternators require these installation steps.

  • Disconnect the negative cable from the battery to avoid shorting.
  • Check the number of terminals on the alternator. They should be two or three, depending on the model. But true one-wire alternators only have one terminal wire connection.
  • Connect the positive or battery terminal to the battery +ve side (usually requires a red wire).
  • Find the negative terminal and connect it to the ground (car body).
  • Some alternators have an ignition terminal. Connect it to the dashboard light’s ignition warning system.

Some things to consider while making these wiring connections include the following.

Wire Size (Gauge Wire)

Pick the appropriate wire size because 1-wire alternators are more sensitive than 3-pin alternators due to their internal regulator.

 If the wire is too thin, it will create a voltage drop that gives false status readings to the regulator. 

A faulty reading can make the alternator not charge the battery.

Use this table as a reference guide for picking the most appropriate wire size.

Gauge per Wire Length
Current (Amperes)Up to 10 inches10-13 inches13-16 inches16-22 inches22-28 inches
75-1008 AWG6 AWG4 AWG4 AWG2 AWG
100-1256 AWG4 AWG2 AWG2 AWG0 AWG
125-1506 AWG4 AWG2 AWG2 AWG0 AWG
150-1754 AWG2 AWG2 AWG0 AWG0 AWG
175-2204 AWG2 AWG0 AWG0 AWG00 AWG

Circuit Protection

We recommend installing a fuse between the battery and alternator to protect the circuit from overloading and damaging either component.

Proper Ground Connection

Paint and corrosion on the car body’s surface can prevent reliable contact with the metal ground. 

So, ensure the ground wire firmly links the alternator and car body.

Alternator Re-Clocking

Some alternators require alternator housing rotation to position the positive terminal in an accessible location. 

You can undo the bolts holding the alternator housing for this positioning but don’t remove the cover. If you do, you will have to reinstall the bushings.

How To Convert a Three-Wire Alternator To a Single-Wire Alternator

If you want to switch from the external voltage regulator setup to a single-wire unit, uninstall this regulator and its extra wires to keep the engine bay clean. 

But you can leave them in place if you plan on reinstalling the three-wire alternator later.

After mounting the alternator, connecting it is easy. Link the charge wire to the positive battery stud terminal, then disconnect the wiring harness from the voltage regulator.

 Leaving it on will keep the indicator dash light on.

A new alternator was installed in the engine, and the belt tensioned around the pulley

A new alternator was installed in the engine, and the belt tensioned around the pulley.

Most of these alternators begin charging at about 1200 RPM because the internal sensory circuit links the battery voltage to the regulator at this speed, switching on the alternator.

So if the engine runs idle and the motor speed + pulley ratio combination does not attain this activation speed, the alternator will not charge the battery. 

The recommended street pulley ratio is 3:1 to eliminate or reduce the low voltage issue at low RPMs.

Wrap Up

In conclusion, one-wire alternators might not be the best for cars, but they have certain advantages that classic and custom car builders admire. 

So if you fall into this category and need a one-wire alternator wiring guide, the article above should help you in the wiring process. 

That’s it for now. Let’s keep the discussion going in the comments section below.

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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