How to Replace a Small Engine Ignition Solenoid

Your battery is fine and you’ve confirmed that the ignition switch is working as well. But when you turn the key, you get nothing. The next, logical, cost effective step is to check out the ignition solenoid.

When it comes to electronic components on the average lawn mower, it’s “shocking” how easy it can all be.

See what I just did there…with the “shocking” thing…?

So, let’s take a minute to talk about one of the most frequently replaced electronic parts of any electric start mower: the Ignition Solenoid.


The ignition solenoid. The ignition coil. It goes by several names. But if your mower has an electronic key start, then your mower has an ignition solenoid; and it looks something like this…

four post solenoid

Now, the purpose of the ignition solenoid is to allow the battery to start your engine. And this is how it works…

As far as the average consumer goes, there are three basic components to the ignition solenoid.

First, there is the battery terminal. The hot wire from the battery attaches to this terminal, providing an electric current to the solenoid.

four post solenoid battery terminal

Battery Terminal

Next, there is the electric starter motor terminal. A wire connects this terminal to the electric starter motor.

four post solenoid starter terminal

Starter Motor Terminal

Next, there is the ignition terminal. The wire from the key start switch attaches to this connector. This allows the key switch to activate the solenoid.

four post solenoid ignition terminal

Ignition Terminal

Finally, there are the mounting brackets…

four post solenoid mounting brackets

Mounting Brackets

…which is how the solenoid mounts to the mower itself. There may be two, or four. Some allow mounting from the bottom or the back. Before purchasing a new solenoid, make sure to confirm how it mounts.


Your battery is connected to the solenoid by a cable that provides a continual source of electricity to the solenoid. But when the electricity reaches the solenoid, it stops. See, that’s what the solenoid does! It acts as a switch that interrupts (and ultimately completes) the electrical flow from the battery to the engine.


So when you turn your ignition key, it sends a small amount of electricity (about 12 volts) to the solenoid. (See that small, red wire attached to the terminal in the front?)


atomicInside of your solenoid is a copper coil wrapped around a metal rod. And our High School science stuff tells us that when you zap a copper coil that’s wrapped around metal, the metal turns into a magnet.

And that’s what happens here!

The electricity from the ignition wire charges that copper coil, which turns that plunger in the middle into a magnet. Then the magnetized metal rod tries to slip up and out of the coil. How? Well, I call it sorcery, but you might call it magnetic force.

solenoid charged

So up goes the plunger. And when it gets high enough it connects with the battery and starter terminals. And you guessed it… the connection is then complete and the electricity from the battery is then allowed to travel to the engine.

And that’s how it works.



Luckily, replacing a solenoid is one of the easiest procedures in lawn mower repair and it pretty much boils down to remembering which “what” was attached to which “where”.

To do this job, you’ll need the following:

socket wrench

3/8” socket & 7/16″ socket

cell phone camera

Cell phone w/ camera (optional)


Before we proceed, let’s make sure your key switch is in the off position and let’s go ahead and use that 7/16″ socket to disconnect the battery.

Got it? Good.

Now, let’s take a look at the solenoid. You’ll see that wires connect to the various terminals by loosening and tightening a nut.

Some solenoids may also have spade connectors as well.

solenoid w spades

It may be a good ideas to snap a quick photo of the entire set up before we start disconnecting things. This will provide a reference when re-connecting everything.

  • Disconnect the Battery cable.
  • Disconnect the Starter cable.
  • Disconnect the Ignition cable.
  • Using your 3/8″ socket, remove the mounting bolts and the old solenoid.
  • Now, reverse the procedure and you’re good to go.

And there you have it! The ignition solenoid in all its glory.

Now go out and enjoy the rest of your day. You’ve earned it.

We carry a large selections of small engine solenoids ready to ship direct to your door.

Do you have questions about small engine ignition solenoids?  Feel free to contact us via phone, email or the comments section below.


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How to replace a lawn mower solenoid
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How to replace a lawn mower solenoid
Replacing a lawn mower solenoid isn't hard if you know the tricks. Read this short article to find out how.
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Bill Brown

Bill is the head of content creation for the LawnMowerPros Blog and DIY section. He’s been in the Outdoor Power Equipment Industry for years and he’s still learning new things everyday. You can often find him creating featured articles, DIY guides, videos, graphics and much more.