What is the purpose of inertia switch fitted to electrical supply fuel pump relay?

The inertia switch fitted to an electrical supply fuel pump relay is a safety device designed to cut off the fuel supply to the engine in the event of a collision. The sudden impact of a crash triggers the switch, breaking the electrical circuit and preventing the fuel pump from operating. This helps to reduce the risk of fire or further injury following an accident by stopping the flow of fuel to the engine. Once the switch is reset (usually manually), the fuel pump can operate normally again.