Remote Radio Controls
WARNING: This page is about a different car, the 2002 Jeep Liberty. However, it is still accessible from the selected car via links, so may be relevant.
These functions are inputs to the Body Control Module and can be read with the DRBIII(R). The switches are a multiplexed signal to the BCM. The radio control MUX circuit is a 5-volt line that is pulled to ground through different value resistors built into the switches. This causes a voltage drop to be seen by the BCM and it sends a specific message to the radio on the PCI Bus circuit. The radio then responds to the message.