Theory Of Operation
WARNING: This page is about a different car, the 2017 RAM 2500 HD. However, it is still accessible from the selected car via links, so may be relevant.
The Radio is provided with a fused Battery and Ground circuit. When the Ignition is turned on, the BCM transmits a wake up signal over the CAN bus to the Radio. The Radio monitors the Speaker, Antenna and Microphone circuits for electrical failures.