AMP Mute Signal Circuit (from Radio Receiver Assembly): Description
WARNING: This page is about a different car, the 2007 Toyota Tacoma. However, it is still accessible from the selected car via links, so may be relevant.
This circuit sends a signal to the stereo component amplifier to mute the noise. Because of that, the noise produced while changing the sound source ceases.
If there is an open in the circuit, noise can be heard from the speaker when changing the sound source. If there is a short in the circuit, even though the stereo component amplifier assembly is normal, no sound or only extremely quiet sound is produced.