Switch unit, steering wheel (633): Activation

The CIM (column integration module) powers the button unit with 5 volts: for audio and telephone on pin 1 and for Sentronic/horn on pin 4. A common ground goes to pin 2. Depending on the switch being pressed, the total resistance will change and therefore also the voltage.

Pin 3 receives a 12 volt PWM signal to control the brightness of the LEDs.

Fig 1: Identifying Communication Flow - Steering Wheel Switch Unit

Courtesy of SAAB-SCANIA OF AMERICA, INC.

Wiring diagram, power supply

Fig 2: Circuit Diagram - Steering Wheel Switch Unit

Courtesy of SAAB-SCANIA OF AMERICA, INC.