One of the good things about having a ride-on lawn mower is that they have electric starters. Say goodbye to yanking on a pull cord! Unfortunately, even electronic ignition systems can go wrong from time to time.
The downside to ride-on mowers is that fixing an electric starter is not as simple as replacing a pull cord on a push mower. So, to figure out why your mower isn’t starting, you’ll have to take a closer look at the lawn mower’s ignition switch. Grab your multimeter, and let’s get to work.
Why Is My Lawn Mower Ignition Switch Not Working? (The Short Answer)
Lawn mower ignition switch problems can be caused by several issues. Problems such as worn-down connections, corrosion of the contacts, an internal short, and the ignition collapsing internally can all cause ignition failure. These ignition problems are usually due to the amount of use they receive and the environments they are subjected to.
Troubleshooting a Broken Lawn Mower Ignition Switch
I like to break down troubleshooting an ignition switch into two categories: external and internal ignition switch problems. Let’s take a look.
External Lawn Mower Ignition Switch Problems
External problems can be caused by different things like a build-up of grime, corrosion, and even the connection becoming loose because of the vibration the switch suffers.
So, first of all, check the connections are in place, and the connector is firmly connected to the back of the ignition. Next, remove the connector and take a look at the pin on the rear of the ignition. These should be free of any rust and not covered in grime, such as oil and dirt.
Finally, take a look at the connector itself. The connector contacts shouldn’t be damaged or have connectors spread open. If the connector can’t make a good, clean and tight electrical connection, then you will end up with a problematic lawn mower ignition switch.
Internal Lawn Mower Ignition Switch Problems
A lawn mower ignition is made up of several rotating metal plates, connectors, a spring, and, of course, the key. To complete different electrical circuits, these parts all need to move in a very specific order, over precise distances, and make firm connections.
They must also be wired correctly to complete their task. Problems with how the key turns between the different positions of the ignition is a sign that there could be a problem internally.
A quick test is to give the key a turn. If it’s either unable to move or moving too easily, it could have collapsed or cannot make the necessary connections.
So, let’s go over how to test a lawn mower ignition switch internally and see if the key is doing its job.
Understanding the Ignition Pins
If you flip over the ignition, you’ll find the 5 pins that connect to the lawn mower’s electrical system. If you take a closer look, you’ll discover that each of the pins is labeled with a letter. Now, the lettering can either be on the housing of the ignition or the actual pin itself. Here’s what the letters stand for.
| Letter | Name | Description |
|---|---|---|
| B | Battery | Positive Connection from the Battery |
| G | Ground | Ground Connection from Either the Battery or the Frame |
| L | Fuel Solenoid | Positive Connection to the Fuel Solenoid |
| M | Magneto | Ground Kill Connection to the Magneto/Coil |
| S | Starter Solenoid | Positive Connection to the Starter Solenoid |
Understanding the Ignition Positions
Next, let’s go over the different positions and the connections the ignition switch makes during operation. Here are the different internal tasks the ignition does while you turn the key.
| Position | Connection | Task |
|---|---|---|
| OFF | G + M | The OFF position makes the connection between the ground and the magneto/coil. This connection grounds the magneto/coil, so the current stops going to the spark plug and kills the engine. |
| RUN | B + L | The RUN position makes a connection between the battery and the fuel solenoid. This connection activates the fuel solenoid so fuel can flow through the carburetor. |
| START | B + S B + L | The START position makes a connection between the battery and the starter solenoid. This connection activates the solenoid to complete the high-current circuit between the battery and the starter motor. The START position makes a connection between the battery and the fuel solenoid. This connection activates the fuel solenoid so that fuel can flow through the carburetor. |
How to Test a Lawn Mower 5-Pin Ignition Switch
To test your lawn mower ignition switch, you’ll need to have a multimeter that can test for continuity. This tests if there is a break in a circuit.
The meter I use makes an audible sound when a connection is made, which I find much easier than using a meter that just has a digital display. Also, a meter that has crocodile clips on each cable makes the testing much less fiddly. So, let’s have a look at the ignition switch test.
Ignition Switch Test Summary
| Position | Test |
|---|---|
| OFF | G - M |
| RUN | B - L |
| START | B - S |
| START | B - L |
Testing the OFF Position G-M
Connect one multimeter cable to the G pin & M pin.
| Key Position | Expected Continuity | Failed Test Results |
|---|---|---|
| OFF | YES | If there is no continuity, then the ignition is faulty and needs to be replaced. |
| RUN | NO | If there is continuity, then there is an electrical short, and the ignition needs to be replaced. |
| START | NO | If there is continuity, then there is an electrical short, and the ignition needs to be replaced. |
Testing the RUN Position B-L
Connect one multimeter cable to the B pin & L pin.
| Key Position | Expected Continuity | Failed Test Results |
|---|---|---|
| OFF | NO | If there is continuity, then there is an electrical short, and the ignition needs to be replaced. |
| RUN | YES | If there is no continuity, then the ignition is faulty and needs to be replaced. |
| START | YES | If there is no continuity, then the ignition is faulty and needs to be replaced. |
Testing the START Position B-S
Connect one multimeter cable to the B pin & S pin.
| Key Position | Expected Continuity | Failed Test Results |
|---|---|---|
| OFF | NO | If there is continuity, then there is an electrical short, and the ignition needs to be replaced. |
| RUN | NO | If there is continuity, then there is an electrical short, and the ignition needs to be replaced. |
| START | YES | If there is no continuity, then the ignition is faulty and needs to be replaced. |
Testing the START Position B-L
Connect one multimeter cable to the B pin & L pin.
| Key Position | Expected Continuity | Failed Test Results |
|---|---|---|
| OFF | NO | If there is continuity, then there is an electrical short, and the ignition needs to be replaced. |
| RUN | YES | If there is no continuity, then the ignition is faulty and needs to be replaced. |
| START | YES | If there is no continuity, then the ignition is faulty and needs to be replaced. |
How to Fix a Faulty Lawn Mower Ignition Switch
Now that you have finished inspecting the wiring of your lawn mower ignition switch and testing the continuity, it’s time to look at the repairs you can carry out. So, here’s what you can do to get your lawn mower running again if you have a lawn mower ignition switch problem.
Corrosion & Dirty Pins
The best product I have found to clean dirt and grimy ignition terminals is an electrical contact cleaner spray. Spraying the contact and then wiping it down with a rag is all you need to do to clean the pins.
For the connector itself, I find spraying the connector and connecting the switch in and out a few times works just fine. If you have some corrosion or rust, then a little piece of sandpaper or file is enough to remove the corrosion.
Tools & Materials to Clean Up Dirty & Corroded Ignition Pins
- Electrical Contact Cleaner Spray
- Cleaning Rag
- Sandpaper/Metal File
Damaged Connectors
If you have some loose connections, then try taking a pair of pliers and pinching the terminal. You’ll be looking to close the connector opening enough so that it will snuggly grip the pins of the ignition switch.
If the connector lacks space to pinch the terminals, then you can try pulling the terminals from the connector. If this isn’t an option and you can’t fix the terminal, then you might need to consider replacing that part of the wiring loom.
Tools to Repair a Connector
- Pliers
Ignition Failed the Continuity Test
Unfortunately, if your ignition switch fails a continuity test, there isn’t much you can do other than replace the switch. So, let’s go over how to wire a lawn mower ignition switch.
First, remove the positive cable from the battery or remove the battery main fuse, if your lawn mower has one. This will protect your new ignition from any shorts or arcs. Then, remove the switch from the dash and disconnect the connector.
Next, mount the new ignition switch into the dash and reconnect the connector. Finally, reconnect the battery or reinstall the main battery fuse.
Tools & Parts to Replace an Ignition switch
- New Ignition Switch
- Screwdriver
- Socket Wrench Set
- Fuse Removing Tool
Are Lawn Mower Ignition Switches Universal?
The short answer is no. The first thing you’ll notice is that ignition switches are available with different numbers of pins. Also, the wiring of lawn mower ignition switches differs from mower to mower. Even if a new ignition switch fits onto your lawn mower and connects to the connector on your mower’s wiring, this doesn’t mean it’s the right switch.
This is why it’s so important to understand the lettering so you can match up a new ignition correctly. So, if your riding lawn mower ignition switch has gone bad, make sure that you either buy a new OEM part (Original Equipment Manufacturer) or check the pins on the replacement ignition.
Very informative, well written! Thank you!
I do all my own repairs and fixing lawnmowers!
Glad you found it useful. Appreciate you stopping by and leaving a comment 🙂
Tom.