I admit it is a stupid idea, but I have seen the auto industry change alot over the years. The auto manufacturer'* don't give a sh*t what is practical and what isn't, all they care about is there bottom line cost. I've worked on well over 5000 vehicles and seen some of the most stupid designs first hand and GM is one of the worst (excluding older models & Bonnevilles).
I have even heard other installers tell me that there is nothing wired through the radio, just to have their customers come back complaining that things aren't functioning in their car.
Also consider this, if the SRS System isn't connected to the factory radio, why do the manufactuers of the $200 harness' (Metra etc.) include instructions on how to disconnect the SRS System before disconnecting power to the factory radio, as well as the fact that you have to count the airbag light flashes to tell if it is still functioning.
It might be a design that GM has changed since, but to my knowledge it is still the same practice that is used. At my current job I install Breath-Anaylizers, Tracking devices & Starters/Alarms (More profit).
I will post what is wired through the radio once I check Mitchell On Demand.
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