Circuit Operation - Steering Wheel Controls

The steering wheel controls consists of two components:
^ Steering Wheel Control Switch
^ SIR Coil Assembly

Steering Wheel Control Switch
The steering wheel switches control both Radio and HVAC functions (Pontiac has only Radio switches). The steering wheel switches are actually a ladder network consisting of the switches and a series of resistors. This ladder network is constructed so that each switch has a different resistance. This arrangement supplies a different voltage output to the radio for each of the switches, when pressed. The radio converts the different HVAC switch selections to serial digital data messages, which are then broadcast to the HVAC system over the E&C serial data link.

SIR Coil Assembly
The SIR coil assembly contains four wires used by the steering wheel controls. This allows voltages from the steering wheel switches to be sent to the radio while the steering wheel is being turned.