I created to wiring harnesses, one for the power and control signals and another for the audio signal going to the radio.
the control harness:
the audio harness:
here is a view of the car, before installing the power/control harness, the plug that is disconnected is the one that goes to the onStar module. It contains all the signals that i need to get.
and here is a view of the harness connected. It is the one going to the right. All the cables are protected with the braid.
Just the standard disclaimer, do not attempt to do this if you do not have the experience and knowledge. The battery does not have the voltage to shock you but has the current to burn you and burn your car. Also the onStar system receives signals from many systems in you car to alert the control center, including information from the air bags. You can damage many expensive subsystems or have a nasty accident messing with this. This is not a recommendation, just a journal with my own experience. I do not encourage you to follow/copy/imitate anything that i do in my own car. It is a good idea to disconnect the battery before you cut/splice any wire in a car.