Remote Radio Switch
WARNING: This page is about a different car, the 2008 Jeep Commander. However, it is still accessible from the selected car via links, so may be relevant.
The six switches in the two remote radio switch units are normally open, resistor multiplexed momentary switches that are hard wired to the Instrument cluster through the clockspring. The instrument cluster sends a five volt reference signal to both switch units on one circuit, and senses the status of all of the switches by reading the voltage drop on a second circuit.
When the instrument cluster senses an input (voltage drop) from any one of the remote radio switches, it sends the proper switch status messages on the Controller Area Network (CAN) data bus to the radio. The electronic circuitry within the radio is programmed to respond to these remote radio switch status messages by adjusting the radio settings as requested.