Steering Wheel Switches
WARNING: This page is about a different car, the 2014 Ford Escape. However, it is still accessible from the selected car via links, so may be relevant.
The RH steering wheel switches contain series of resistors. Each steering wheel switch function corresponds with a specific resistance value within the switch.
The FCDIM sends a 5-volt reference voltage to the RH steering wheel switches on the input circuits. When a switch is pressed, the voltage is routed through the corresponding resistor(s), and then to ground through the FCDIM . The FCDIM monitors the resultant voltage drop to determine which switch was pressed. The voltage drop varies depending upon the resistance of the specific switch pressed.
The steering wheel switch inputs are sent as network messages from the FCDIM to the ACM to control audio functions.