The Safety System Switches were located in the Control Room of the Isla Nublar Visitor Center. These were manually operated, preventing the computers from being shut down unless they were turned off by hand. They were located on the main panel, and had metal swing-latches over them to prevent an accidental activation. The switches had to be shut off in order, with the Master Switch being last to be shut off in order to turn off the power. After shutting off the switches, it was necessary to wait thirty seconds for the system to reboot until the switches could be turned back on in order to restart the power.
Jurassic Park by Michael Crichton page 256-257 (First Edition, Thirty Fourth printing)