Cruise control is a system that automatically controls the rate of motion of a motor vehicle. The driver sets the speed and the system will take over the throttle of the car to maintain the same speed. (wikipedia.org).
The following article contains detail information about Toyota Yaris 2007 Cruise Control System. This articles provides description and illustration on how the cruise control works, system diagrams (includes stop light switch, cruise control main switch, spiral cable, combination meter assembly, speed sensor, ECM, neutral position switch, throttle body assembly, and DLC3), cruise control parts location, fault diagnosis, troubleshooting and repair procedures for problems encountered during the operation of Yaris.
The cruise control system makes it possible to drive at a desired speed without using the accelerator pedal. The ECM controls the throttle opening angle based on signals from switches and sensors. The microcomputer which controls the cruise control system is built into the ECM, and uses is the throttle position sensor and motor as the actuator. Constant speed control gets ready when the cruise control main switch ON-OFF button is pushed (the CRUISE MAIN indicator light comes on).
Find more information about 2007 Toyota Yaris Cruise Control System – Service and Troubleshooting here – 42 pages of PDF filetype. (source: scribd.com, wikipedia.org). Find also other Toyota Wiring Diagram you might be looking for.