Lawn Mower Ignition Switch Problems – Troubleshooting and Fixes

The ignition switch is the part of your lawn mower that powers on the mower’s engine. As such, if your mower fails to start, it’s likely that there’s a problem with the ignition switch. 

Most ignition switch problems can be traced to bad wiring or a faulty solenoid. Common fixes include properly wiring the terminals, replacing the ignition coil, and replacing the ignition switch.

We’ll show you signs of a problematic lawn mower ignition switch and possible solutions to make your yard work easier.

How does a lawn mower ignition switch work?

To understand a lawn mower’s ignition switch problems, you have to understand how power goes from the switch to the engine. 

The four-point process starts with you turning the key to START. The ignition switch sends electrical signals to the solenoid’s coil. The coil derives power from the battery cable, closes the circuit, and sends the power to the starting motor. 

The motor then sets the engine spinning. 

Signs of lawn mower ignition switch problems

A well-functioning lawn mower should power on as soon as you turn the ignition switch. However, the following problems should be an indication of a problematic ignition switch. 

  • The ignition key sticking.
  • The engine doesn’t turn on. 
  • You are unable to easily move the ignition key back and forth between OFF, RUN, and START potion.
  • The engine cranks briefly then goes off. 

Other symptoms of lawn mower ignition problems include the mower overheating, the mower stalling, and the engine not turning off unless you disengage the spark plug.

Common Lawn Mower Ignition Problems + Fixes

Common lawn mower ignition problems include loose or severed wires, a faulty starter solenoid. You can fix the above lawn mower ignition issues by properly connecting the wires and replacing the ignition switch with a new one.

Mower Ignition Problem #1: Ignition Switch Wiring Issue

If your mower runs for a while and then abruptly comes to a halt, it’s likely there’s an issue with the wire connections. Loose wiring might be preventing enough current from reaching the solenoid.

It could also be due to the ignition switch’s ground terminal being disconnected from where it’s grounding. Another possibility is that the kill switch wire could be loosely connected and touching against the body of the mower.

Note: Disconnected wires within the ignition module may also cause your engine to crank but still fail to fully start.

Mower Ignition Problem #2: Faulty Ignition Coil/Solenoid 

Your lawn mower may have a starter coil problem if it tends to suddenly shut down as you’re mowing and you can’t restart it until it cools down. If the ignition coil is faulty, it won’t be able to effectively spin the flywheel. Consequently,  it won’t engage the crankshaft, resulting in engine start-up failure or abrupt halting.

Note: Other causes of ignition coil failure include vibration and heat. Also, if other components of the ignition system such as the wires or the spark plug are worn out, the coil becomes overworked. An overworked coil leads to reduced lawn mower lifespan. 

Mower Ignition Fix #1: Ensure the Wires are properly connected

Here`s how to troubleshoot and fix wiring connection issues;

i.    Locate the Ignition Switch Components

First, you need to find the location of connections and components of the ignition switch. Use the circuit diagram in the product manufacturer’s instruction manual to access the components and connections faster

The circuit diagram includes the layout of all the electrical connections between the lawn mower components. This schematic will help you locate the battery, solenoid, the lights, and the magneto coil.

Note: If you’ve misplaced your instruction manual, you can find a soft copy online by looking up the mower’s brand name and model as search keywords.

ii.     Connect the Switch to the Ground

Next, connect the switch’s ground terminal marked ‘G’ to the solenoid’s ground terminal or the negative end of the battery. You can use a multimeter to confirm if the connection is good.

iii.   Connect the Switch to the Solenoid

Wire the switch terminal marked ‘S’ to the solenoid’s positive terminal. Use alligator clamps or soldering iron to connect wires to their respective terminals. 

iv.    Connect the Magneto to the Switch

Wire the ignition switch’s ‘M’ terminal to the magneto’s open terminal.

v.     Connect the Battery

Connect the ‘B’ terminal of the ignition switch to the positive terminal of the battery to provide voltage.

vi.   Connect the Lights/Accessories

Wire the lights to the ‘L’ terminal of your ignition switch. This ‘L’ terminal is marked as ‘Y’ in some ignition switches 

vii.   Secure the Switch in Place

Secure the ignition switch in position with a screwdriver once you complete all the connections. Ensure all screws are in place. Replace the plastic/rubber casing.

viii.    Test the lawn mower

With the ignition switch connection issues fixed, start the mower to see if it starts and functions properly. If your lawn mower still doesn’t start or stalls even after fixing the ignition switch issues, it could be that the battery terminals are corroded thus limiting the passage of current.

Pro Tip: Pour a few drops of Coca-Cola soda on the terminals to fix corrosion. Alternatively, you can use a wire brush and sandpaper to scrub away deposits.

Mower Ignition Fix #2: Replace the Ignition Switch

If the ignition switch is faulty (for instance, due to worn-out terminals), you’ll have to replace it. Follow the procedure detailed below to replace a faulty lawn mower ignition switch.

i.   Detach the battery: Turn the ignition key to the ‘OFF’ position and pull it out from the ignition switch. Then, lift your mower seat and then disconnect the negative terminal from the battery by removing the bolt that secures it in place.

ii.   Pull out the ignition switch: Lift the hood and find the locking tabs located at the back of the ignition switch. Release the tabs and push out the switch.

iii.    Detach the wire harness: Pull out the wire harness from the back of the ignition switch.

iv.    Install the replacement switch: Reattach the wire harness that you’d detached from the old ignition switch to the back of the new switch. Then insert the new switch back into the dash and secure it using the locking tabs before closing the hood.

v.    Reconnect the battery: Wire the ignition switch’s negative cable back to the battery’s negative terminal.

Mower Ignition Fix #3: Replace the Ignition Coil

If your lawnmower won’t start due to a defective ignition coil, you need to replace the coil. 

  1. Remove the spark plug and let it touch against the engine block. Then, try to start the engine and check for sparks. If there is no spark, then the ignition coil is bad and should be replaced.
  2.  Disassemble the mower parts until you gain access to the flywheel and the ignition coil. Then, unscrew the faulty ignition coil, while also ensuring to detach the kill switch wire connected to it. 
  3. Next, take your replacement ignition coil and reconnect the kill switch wire, before screwing the ignition coil to secure it in place.
  4. When attaching the new ignition coil, you should loosely screw it down such that it can move back and forth. This will allow you to leave just enough space — 0.1-0.3 mm— between the coil and the magnets on the flywheel. 

Tip: To create this narrow gap, fold a piece of paper and insert it between the flywheel and the ignition coil. 

  1. At this point, you can now tighten the screws, before spinning the flywheel to remove the piece of paper. 
  2. Finally, reattach all the casings before starting the mower again to see if the new ignition coil has solved the problem.

Tests for mower ignition switch problems

Use a digital multimeter to check for circuit completion between the battery and the starter solenoid when you test for mower ignition switch problems. Another test method entails monitoring the warning lights on your mower.

Method #1: Starter Solenoid Test

i.   Insert the key into the ignition switch.

ii.  Next, connect the positive terminal of a multimeter to the power supply, with the negative end connected to the base of the starter solenoid/distributor.

iii.   Then, turn the ignition key to the running position. Check the voltage reading of the battery on the multimeter. The voltage reading should be at least 90% of the main battery’s voltage. If it’s lower, it means there’s a problem with the ignition switch or wires.

Method #2: Warning Lights Test

Insert the ignition key into the ignition switch and turn it to the ‘START’ position. 

As soon as the engine starts to crank, let go of the key so that it automatically snaps back to the ‘RUN’ position. At this point, you should be keeping track of the warning lights. If they go off, then you have a faulty ignition switch.

Method #3: Magneto Test

 You can test for magneto failure using a digital multimeter and alligator clamps. Set the multimeter to ‘ohms’ and turn the ignition key to the ‘OFF’ position. Check for continuity between the ground terminal (marked ‘G’) and the magneto terminal (marked ‘M’).

If there’s a beep, then this component is okay. If not, then the issue could be magneto failure.

Tips for maintaining the ignition switch

i.  Ensure you regularly clean corroded terminals using a wire brush and sandpaper to prevent current blockage. 

ii.  Professional machine servicing entails troubleshooting and repairing all faulty parts of the lawnmower, including the ignition switch. We recommend a mandatory annual full servicing on the lawnmower. 


i. Universal Technical Institute: What is Battery Terminal Corrosion?

ii. Wikipedia: Starter Solenoid

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