GM Service Manual Online
For 1990-2009 cars only
Figure 1:

Power, Ground, Serial Data, Antenna and Front Speaker Outputs


Object Number: 2080954  Size: FS
Figure 2:

Rear Speaker Outputs


Object Number: 2080957  Size: FS
Figure 3:

Steering Wheel Radio Redundant Controls


Object Number: 2080961  Size: FS