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Starter Solenoid gets activated by pressing the ignition button or turning the key. When the current starts flowing from the battery to the solenoid, it creates the magnetic field inside and closes a higher current circuit for your motor to engage.

A starter solenoid is one of the key components of an engine starter motor. These motors are used in internal combustion engines to start them up (as their name suggests).

In cars, when the ignition key is switched to ON (or the “engine start” button is pressed), the starter motor begins to rotate, and by the action of a pinion on the engine’s flywheel ring gear, the crankshaft begins to spin.


The engine then begins soaking up air and fuel, and finally starts up in the minute as one of the cylinders ignites the air-fuel mixture. Starter solenoids are key components of modern starter motors and this is why so many people want to know how they work.

Some mechanics refer to solenoids wrongly, as if they were talking about the starter motor itself, and not about one of its components.

Working of a starter solenoid

I think that knowing what a starter solenoid does is as relevant as it works. It could be said that a starter solenoid basically is just the same as any other solenoid.


A “Starter Solenoid” working principle in physical terms is described in this post: “What does a Solenoid Do?” and if you haven’t read this article, I would suggest you read it first. It will give you a better understanding of the topics explained here.

From the technical point of view, and regarding the construction of a solenoid, there are some characteristics that make these kinds of actuators special. The first and most important difference between them and regular solenoids is that they perform two functions at the same time.

On one end, they have a plunger that closes the circuit of the starter motor, turning it on. At the other end, they have another plunger that is attached to a mechanical part called “operating fork”, which is the piece that makes the pinion engage with the ring gear located on the engine’s flywheel.

When the power to the starter solenoid is cut, and aided by a spring, the plungers disengage the starter motor from the engine and shut the current off, causing the starter motor to stop.

This video will help you to understand how a starter motor works and why the use of a starter solenoid  is so important

Construction of a Solenoid

Starter solenoids are designed to handle big amounts of power and that’s why their coil is made of very thick copper wire. This wire is heavy enough to endure the high currents that it manages and is able to activate the operating fork every time for the many thousands of cycles that an engine was started over its operative life.

Let’s take a look at what is inside of the starter solenoid as it gets opened up:

The starter solenoid is activated by a small amount of electrical current, which enables the ignition switch to be connected by using thinner wires. This makes all the high current circulation occur only inside the engine bay and keeps the high current far away from the operator, who is turning the ignition key or pressing down the ignition button.

Wiring like this makes the whole startup process, safe. Here is Starter Motor and Starter Solenoid wiring diagram:

Looking for a starter solenoid? Yes, they are also sold on Amazon! What isn’t ????? Here are some starter solenoids (paid link) that will be delivered straight to your house…

This article is for informational purposes ONLY and is NOT a replacement for professional advice!

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