From the Prius System Diagram document it shows Mute being on L19 harness on Pin 17 if I'm reading these correctly. I have all the Prius Manuals but I can't seem to figure out how one figures out where all these various harnesses are on the car. How does one go about trying to figure that out? A pointer to where is the L19 harness is would be appreciated?
There should be a drawing of the car in the wiring diagram that points out the L19 connector location.
L19 seems to connect to the Safety Connect Transceiver (note all the *8's in the diagram, including the mute wire). I don't believe your III has Safety Connect, so you will never find the connector or those wires.
Here is a diagram showing the location if you did have it in your vehicle...looks like it would be in the area beneath the head unit/AC controls...
