Inertia Fuel Shut-off (IFS) Switch
WARNING: This page does not describe the selected car, but rather 32 other vehicles, including the 2011 Mercury Milan, 2011 Mercury Mariner, 2011 Mercury Grand Marquis, 2011 Lincoln Town Car, and 2011 Lincoln Navigator L. However, it is still accessible from the selected car via links, so may be relevant.
The IFS switch is used in conjunction with the electric fuel pump. The IFS switch shuts OFF the fuel pump if a collision occurs. It consists of an inverted pendulum mass that is retained in a conical cone through a set of linear springs. When a sharp impact occurs, the pendulum shifts out of the conical cone, opens the circuit and shuts OFF the electric fuel pump. Once the switch is open, it must be manually reset before restarting the vehicle.