Lexus GS300 1998 Owner's Manual page 294

Turning on the system
31G011
To operate the cruise control, push the main switch. This
turns the system on. The indicator light in the instrument
cluster shows that you can now set your desired cruising
speed. Another push on the switch will turn the system
completely off.
When the ignition key is turned off, the main switch is also
automatically turned off. To use the cruise control again, push
the main switch again to turn it on.
CAUTION
To avoid accidental cruise control engagement, keep the main
switch off when not using the cruise control.
STARTING AND DRIVING
281