Here are some answers to the more common questions that I have received.
The radio goes into TELEPHONE mode when the MUTE pin is grounded, if you do not have the onStar system this is almost all what you need to know. If you do have the onStar system and want to keep it operational (good idea even if you do not subscribe) then more work is required.
The audio harness and the control harness will go to a circuit that I’m designing with the help of my good friend SQ. It is mostly based on what I posted before.
The circuit will use as a part of it the “guts” of the belkin car adaptor. The adaptor provides the iPod connector and a variable gain amplifier to adjust the signal levels coming from the iPod to the level required by the radio.
The circuit will have a switch that will do normal operation, or activate the input. Additional logic is required to allow the onStar system to override the settings in case it goes active.
As an enhancement I decided to add a second input that can be used for an XM/Sirius radio, a scanner or any other device. Then the final system will have a switch with three positions, iPod, normal, AUX.
The circuit also contains an attenuator to adjust the signal level coming form the onStar system to the lower signal now required.
Here is a link to a preliminary circuit. I assembled that circuit on a proto-board and plan to test it tonight. The output audio output of my circuit goes into the input of the belkin adaptor and then to the radio.
I plan to fit all the circuits inside the cell phone holder that I ordered from the saab catalog. Under that holder I will put the little switch and a 1/8 stereo jack for the second AUX signal.