Jim!
Yea, I never figured anything about sending data thru the CDM. When I did mine 5 yrs ago it was during the winter so i just left the car sit while waiting for all the audio parts to come back. I just last week learned about the data lines when I took the box out of my friend's car and he was repairing the A/C system at the same time. He got no response from the A/C control head and read about it in the FSM, section 8A.
I will say this much about doing anything with the CDM box..reconnecting the antenna jack is the hardest connection to do in this whole deal. If the antenna lead is not oriented just right, you can't get the plug to seat fully into the socket. It's so frustrating, or it was to me anyway.
Good luck with the repair!
Tom