Switching Off Cruise Control: Function
WARNING: This page does not describe the selected car, but rather 10 other vehicles, including the 2004 Land Rover Discovery, 2003 Land Rover Discovery, 2002 Land Rover Range Rover, 2002 Land Rover Discovery, and 2001 Land Rover Range Rover. However, it is still accessible from the selected car via links, so may be relevant.
When the cruise control master switch is turned off, the cruise control ECU switches off power to the vacuum pump assembly. The vacuum dump valve opens releasing the vacuum in the pneumatic actuator, returning the throttle disc to driver control via the accelerator pedal.