How To Test Lawn Mower Ignition Switch(In 5 Quick Steps)

Testing your lawn mower ignition switch is straightforward and can be done using a multimeter and a few basic tools. In this guide, you’ll learn how to safely test, diagnose, and confirm whether your ignition switch is the problem or if the issue lies elsewhere.

How to Test Lawn Mower Ignition Switch

Safety First:

Before you start testing, take a few precautions:

Remove the spark plug wire from the plug to prevent accidental starting.
Park the mower on a flat, stable surface.
Engage the parking brake.
Wear gloves and safety glasses.
Disconnect the negative battery cable if the mower has one.

Tools You’ll Need:

Multimeter (set to continuity and voltage modes)
Screwdrivers (flathead and Phillips)
Socket wrench set
Electrical contact cleaner
Needle-nose pliers
Replacement ignition switch (if the old one fails the test)

Step 1: Visual Inspection

Before grabbing your multimeter, start with a simple check:

Inspect the ignition switch and the surrounding wiring for signs of corrosion, melting, or loose connections.
Ensure the ignition key turns smoothly and doesn’t stick.
Look for burned or discolored wires near the switch, which could indicate short circuits.

If everything looks fine, proceed with electrical testing.

Step 2: Identify the Ignition Terminals

Most ignition switches have multiple terminals labeled as:

B (Battery) – Power input
S (Starter) – Sends voltage to the starter solenoid
M (Magneto or Coil) – Grounds the ignition coil to shut off the engine
G (Ground) – Ground connection
L (Lights/Accessory) – Controls lights or accessories

Step 3: Continuity Test (Switch Off the Battery)

Set the multimeter to continuity (Ω) mode.
With the key in the OFF position, test between:
- B and M – You should have continuity (the circuit is closed to ground).
Turn the key to RUN (ON) and retest:
- B and M should now show no continuity (open circuit).
Turn the key to START and check between B and S – You should now have continuity.

If the readings differ from these expected results, your ignition switch is faulty.

Step 4: Voltage Test (Battery Connected)

Reconnect the mower battery.
Set the multimeter to DC volts.
Turn the key to RUN and check the voltage at the B and S terminals. You should read about 12 volts.
If voltage is present at B but not at S when starting, the switch is failing to send power to the starter circuit.

Step 5: Ignition Coil Ground Test

When the ignition key is turned OFF, the M (magneto) terminal grounds the ignition coil to stop sparking. To test:

Disconnect the wire leading from the ignition switch to the coil.
With the key OFF, check for continuity between the M terminal and ground — there should be continuity.
With the key ON, there should be no continuity (the ground path is open, allowing spark).

If the ground path doesn’t behave as expected, the ignition switch is bad.

Step 6: Replace the Faulty Switch

If your ignition switch fails the continuity or voltage test, replace it.

Label all wires before disconnecting them.
Remove the mounting nut or screws and pull out the old switch.
Install the new switch, reconnect wires, and test the mower.

A new ignition switch is inexpensive and easy to replace, restoring reliable starts to your mower.

FAQs

How to tell if a mower ignition switch is bad?

A bad ignition switch often shows symptoms like:

Turning the key does nothing, no click or crank.
Accessories like headlights don’t power on.
The starter motor receives no voltage even with a good battery.
The mower only starts intermittently or shuts off unexpectedly.
Testing continuity with a multimeter can confirm the diagnosis.

How to test an ignition switch with a multimeter?

Set your multimeter to continuity mode. With the battery disconnected:

Place one probe on the B (battery) terminal.
Touch the other probe to the S (starter) terminal.
Turn the key to START — you should hear a beep or see a reading near zero ohms (closed circuit).
If not, the switch isn’t completing the circuit and needs replacement.

How to find out if your ignition switch is bad?

If your mower doesn’t start despite a charged battery and a functional starter solenoid, suspect the ignition switch. Test it by checking continuity and voltage across terminals in different key positions. A lack of voltage to the starter or coil terminal when turning the key means the switch is defective.

When I turn the key on my mower and nothing happens?

If nothing happens when you turn the key, check:

The battery (ensure it’s charged).
Battery terminals and ground connections.
Fuse (if equipped).
Seat and brake safety switches.
If all are functional, the ignition switch may not be sending power to the starter solenoid, indicating it’s bad.

How do I know if my ignition coil is bad on my lawn mower?

A failing ignition coil won’t produce a spark. To check:

Remove the spark plug and reconnect it to the plug wire.
Hold the plug against a metal part of the engine.
Crank the engine and watch for a spark.
No spark means either the coil is bad or it’s being grounded by a faulty ignition switch or kill wire.

How does a lawn mower ignition system work?

A lawn mower ignition system uses the flywheel magnet to generate voltage in the ignition coil as it spins. The coil sends high voltage to the spark plug at the right moment, igniting the fuel-air mixture. The ignition switch controls power flow. Turning it ON allows spark; turning it OFF grounds the coil to stop spark and shut off the engine.

Final words

Testing your lawn mower ignition switch is a simple but essential maintenance skill. By following the continuity and voltage tests outlined above, you can quickly determine whether the switch, wiring, or another component is preventing your mower from starting.

Replacing a faulty switch is inexpensive, restores reliability, and keeps your mower running smoothly through the season.

How to Test Lawn Mower Ignition Switch(In 5 Quick Steps)