figuring it out

i removed the radio to see if i can find any clues, here is a photo of the label on the top:



some interesting clues here, a "TEL MUTE", "TEL IN", "TEL GND" pins, i hope all are inputs.

Time to get the voltmeter and if it gets complicated then our friend the o-scope!

observations:

* the TEL-MUTE pin shows a 4.76 V, continuously and goes to 0V when the telephone (on-star) is active. Can it be that easy?

* using a set of headphones i monitored the TEL-IN and TEL-GND, looks like a standard analog audio line signal.

things look promising, back to the car...