How to Replace a Lawn Mower Safety Switch

 

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This DIY lawn mower repair guide has step-by-step instructions for how to replace a lawn mower engine safety switch. The safety switch stops the engine when you release the control bar on the handle, by stopping the ignition coil from sparking; it also has a brake pad to slow the flywheel. If the switch isn't working, the ignition coil won't spark the spark plug, and the lawn mower won't start.

To determine if the switch is the problem, remove the kill wire from the ignition coil and check for engine spark. If there's spark, replace the engine safety switch with the manufacturer-approved replacement part.

A broken safety switch can also make the ignition coil keep sparking after you release the handle lever. In that case, remove the spark plug until you can replace the mower engine safety switch.

This procedure works for Briggs & Stratton engines that power Craftsman, Poulan, MTD, Troybilt, Toro, Husqvarna, Murray, Yard-Man and Snapper walk-behind lawn mowers.

Repair difficulty:
     
Time required:

Less than 30 min.

Parts required

  • Engine safety switch

For manuals, repair guides, and specific part recommendations, enter your model number.

Tools required

  • Phillips screwdriver
  • Socket wrench
  • 5/16" socket
  • 3/8" socket
  • Needle-nose pliers
  • Slot screwdriver

Before you begin

Let the engine cool. Wear gloves to protect your hands.

Instructions

 Warning: Undertaking repairs to appliances can be hazardous. Use the proper tools and safety equipment noted in the guide and follow all instructions. Do not proceed until you are confident that you understand all of the steps and are capable of completing the repair. Some repairs should only be performed by a qualified technician.

Step 1: Disconnect the spark plug wire

Disconnect the spark wire so there's no chance that the mower could accidentally start.

Disconnect the spark plug wire.

Step 2: Remove the starter rope from the guide

Remove the starter rope from the rope guide. If the rope won't slip past the guide and the handle, loosen the guide.

Remove the starter rope from the guide.

Step 3: Remove the engine cover

Remove the screws securing the engine cover to the engine. Slide the rope through the hole in the engine cover. 

Remove the engine cover.

Step 4: Remove the fuel tank

Remove the screws that secure the fuel tank to the engine. Lift the tank off, being careful to keep the fuel tank upright so it doesn't leak. 

Remove the fuel tank.

Step 5: Remove the dipstick

Remove the screw that secures the dipstick tube to the housing. Remove the dipstick from the engine and plug the hole with a paper towel to keep debris from falling into the engine.

Remove the dip stick

Step 6: Remove engine blower housing

Remove the bolts securing the blower housing to the engine and remove the housing from the engine.

Remove the engine blower housing.

Step 7: Remove the zone control cable

Take a digital photo of how the zone control cable connects to the engine safety switch. Use a pair of needle-nose pliers to squeeze the tabs on the cable housing. Pull the cable housing to remove it from the safety switch bracket. 

Remove the zone control table.

Step 8: Remove the kill wire from the safety switch

Press down on the tab that attaches the kill wire to the safety switch and disconnect the wire from the safety switch.

Remove the ignition kill wire.

Step 9: Remove the safety switch

Remove the 2 mounting screws that secure the engine safety switch to the engine. Remove the safety switch.

Remove the safety switch.

Step 10: Install the new safety switch

Position the new safety switch onto the engine and secure it with the mounting screws. 

Step 11: Reinstall kill wire and zone cable

Reinstall the kill wire by pushing down the locking tab and inserting the wire into the safety switch. Release the tab.

Reconnect the zone control cable and work the engine control bail on the handle to make sure it works smoothly. 

Step 12: Reassemble the mower parts

Position the engine blower housing on the engine and bolt it into place.

Remove the paper towel from the dipstick opening, slide the dipstick into the engine and secure it with the screw.

Feed the starter rope handle through the engine cover up to the rope guide.

Position the engine cover on the engine and screw it into place.

Step 13: Reconnect the spark plug wire

Attach the spark plug wire and make sure the mower works properly.