What Is W Terminal On An Alternator? (With D+, DFM, R, E, F)

what is w terminal on an alternator

Even though alternators play a critical role in the operations of an engine, the average consumer will be hard-pressed to explain how they work. As such, no one expects you to know what the W terminal is or where you can find it.

More than likely, you can get by without knowing what the W terminal does. After all, most drivers prefer to leave defective alternators in the hands of experts. But if you’re determined to understand the workings of an alternator, this guide will give you all the information you need.

What Is W Terminal On An Alternator?

The W terminal drives the tachometer. To be more specific, it is the output signal to the tachometer. An expert will tell you that it creates an AC voltage whose frequency is proportional to the rotational speed of the engine.

The tachometer measures the engine’s working speed. If you’ve ever wanted to know how hard an engine is working, a tachometer will you.

You don’t want the engine to run too fast or too slow. And if it is, the tachometer will warn you, giving you plenty of time to resolve common issues such as poor lubrication.

Some tachometers are analog. Others are digital. Some require direct contact with the relevant rotating parts of the engine. Others use a laser. Every vehicle requires a tachometer to identify and resolve problems with the engine speed before they become worse.

Where Is W Terminal On An Alternator?

The new alternator might not have a W terminal. If you want to know where it is, look near the bottom of the alternator. Your target is a short, thin, blue wire with a push-disconnect connection. Don’t expect plugs and clamps.

The W terminal will only become difficult to locate if you replace the alternator.

Don’t expect every car to have a W terminal. Some vehicles have a W terminal that drives the dynamic oil pressure system. Others do not have one.

How To Test W Terminal On Alternator?

You don’t need to test alternators. Once they malfunction, you are better off getting a new one, especially if the car won’t start. But you can take certain steps to check the viability of a faulty alternator.

Most people start by reaching for a voltmeter for a good reason. They are cheap and effective. Because you can’t test the alternator if the battery is too low, you have to make the battery a priority.

Open the hood and attach the leads to the terminals. The red lead goes to the positive terminal and the black lead to the negative.

If the battery is healthy, use the alternator gauge to study the alternator output. This involves running the engine and activating all the electronic accessories in the car. Be sure to rev the engine to 2000RPM.

The objective is to observe the response of the alternator when you strain it. You can also listen to the device while running the engine to determine whether or not it squeaks and squeals unnaturally.

Sometimes, the alternator is at fault. Like every other item in a vehicle, alternators will eventually fail. But in other cases, you have to blame the battery.

A worn-out battery will strain the alternator because it has to work so much harder to keep up with the demands of the battery. As a result, the alternator may overcharge the battery.

Overcharging sounds like a good thing, but it isn’t. The battery case will start swelling. It will also overheat. You can create an overcharging condition by improperly jumpstarting a car and disrupting the alternator’s wiring with the resulting surge.

You can cause just as many problems by installing the wrong alternator. You ran the risk of supplying more charge than the existing demand, creating an overcharge condition. This is less of an issue for consumers with newer alternators because they have mechanisms that control the voltage.

Wikihow has images and videos that explore these investigative processes in greater detail.

Some Other Terminals Meaning

  • D+

D+ is the battery connector. D+ is the positive connection. D is the negative connection. You can see this symbol on European alternators. They associate D+ with the indicator light circuit. Some alternators use ‘61’ instead of D+.

  • DFM

The letters, which stand for ‘Digital Field Monitor,’ refer to a connection to the ECU of a vehicle. You could also describe it as a block signal that travels between the alternator and ECU.

Don’t expect to see DFM in every alternator. Some vehicles use ‘FR,’ ‘LI,’ or ‘DF.’

  • R

This is the relay terminal. It works with the alternator to power accessories like the tachometer, hour meter, and dash light.

  • E

‘E’ is associated with excitation. This is the warning light.

  • F

This is the full-field bypass for the regulator. You will see it in externally regulated devices.

  • FR

The ECU gets information about the charge rate from this connection. You can find this terminal in older models from Japan.

  • G

This is the chassis negative connection. The ECU turns to the G terminal when it needs to control the voltage.

  • I

This is the indicator

  • L

This one stands for ‘Lamp,’ or more specifically, warning lamp. It will close the circuit to the warning lamp. This is not the only symbol associated with the warning light circuit connection. Check your manual for clarification.

  • M

This connection stands for ‘Field.’ Don’t expect to find it on every alternator. It is common among old externally regulated models.

  • N

This is the neutral

  • P

Alternators put out a pulse on the P terminal. These units can run the tachometer via the P terminal. This is why people call it the stator connection for a tach.

  • R

This is the relay terminal. It provides some of the output the alternator uses to operate various accessories, including the dash light.

  • S

This is the battery sense connection (Battery Voltage Sense Wire). It links directly to the battery, creating a charging fault if the connection is absent. The S terminal will measure the voltage.

  • T

This stands for the tach. As you may have guessed, it is the terminal for the tachometer.

  • Field

Alternators have a field wire that sends power to the rotating field coil. How-Stuff-Works has mentioned alternating finger pole pieces surrounding the rotor shaft’s iron core. These coil wires are a critical component of an alternator.

You can define the F and M terminals as the field. They are both associated with externally regulated alternators. Although, M is typically found in older units.

  • Aux

AC alternators have an auxiliary wound excitation mechanism that works with a second winding, acting as an independent power source to the AVR. Some alternators don’t have an aux terminal.

You will find aux wires in older alternators that must be excited before they can charge. Aux connections are unnecessary for newer models that don’t require excitation.

You can check the diagram that comes with the alternator to determine whether or not the aux terminal should be present.

The Use Of Identifying Alternator Terminals

Alternator terminals are wide-ranging. The terminals above are a small portion of the many connections you will encounter on an alternator. Others include A (battery), B (battery), COM (computer connection), W (waveform), B+ (battery), etc.

You must identify the terminals to configure, troubleshoot and repair your alternators. Alternators are complicated devices to troubleshoot, especially for the layperson, because they have so many parts, including vents for heat dissipation and drive pulleys.

You cannot configure the alternator if you don’t know what the terminals are, how to locate them, and the best way to test them.

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