Normal Operation
WARNING: This page is about a different car, the 2004 Mercury Mountaineer and 2004 Ford Explorer. However, it is still accessible from the selected car via links, so may be relevant.
The steering wheel audio control switch(es) consist of a specific resistor value for each button function creating a voltage divider. When a button is pressed, a specific reference voltage is sent to the audio unit. The audio unit then uses this reference voltage to determine which control input function has been selected. Circuit 583 (YE) is the reference voltage circuit between the steering wheel audio controls and the audio unit. The ground circuit for the steering wheel audio controls is through the PCM, circuit 848 (DG/OG).