This DIY riding mower repair guide gives step-by-step instructions for replacing the seat on a riding lawn mower. For safety, a switch in the riding mower seat allows the mower to run only when it senses that someone is on the seat. If the seat is cracked or the foam cushioning inside the seat is missing or broken down, the seat switch might not engage when you’re in the seat. In that case, the engine shuts off when you release the brake. To fix the problem, replace the seat with a manufacturer-approved replacement part.