Larger lawn mowers, such as riding mowers and lawn tractors, have a kill switch system. It's related to the ignition system and is designed to keep the rider safe and prevent harm to others. If something compromises the kill switch or related systems, it can endanger people or damage your mower.
The kill switch is typically located underneath the operator seat. It's also referred to as the safety switch since it's designed to shut off major systems if a rider leaves the seat. To identify if there is a kill switch problem, examine your operator's manual for conditions that would normally engage it, such as leaving the seat when the PTO blade is engaged. Test this by engaging the PTO and standing up from your seat slightly. If the PTO doesn't shut off, the switch may need to be replaced.
The ignition switch is the first step in the electrical starting system. Once the switch is activated via electric start or key ignition, an inside connection between two poles creates an electrical signal that's relayed to the magneto. A faulty or shorted switch won't disconnect the poles, keeping your motor running despite the "off" command. Because of its size and design, a faulty switch should be replaced and not repaired
The magneto relays the signal from the ignition switch to the spark plug. Magnetos are made up of two metal coils and an armature. When a flywheel moves the magnet by the armature, it generates electricity in the first coil. Once a specific limit is reached and trips a circuit breaker, the first coil sends electricity to the second coil, which amplifies it and sends it through the spark plug. A faulty circuit breaker will keep the electricity going instead of shutting off the spark plug.
Both the ignition and kill switch systems have positive and negative wiring to related parts like the magneto, spark plug or PTO. Examine those wires for obvious damage like exposed wiring, tears or arcing. Also check any related ground wiring, which is designed to keep electricity from leaving discharging outside of the system. If your lawn mower runs these wires through an electrical control unit, also check the fuses to see if they have blown.