Normal Operation
WARNING: This page is about a different car, the 2005 Mercury Mountaineer and 2005 Ford Explorer. However, it is still accessible from the selected car via links, so may be relevant.
The steering wheel audio control switch consists 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 powertrain control module (PCM) circuit 848 (DG/OG).