OS-1

• Applications: The OS-1 is an interface that allows for the replacement of a GM factory radio that doesn't have RDS, while maintaining the operation of the OnStar navigational system. The OS-1 has onboard switching and amplification that allows the audio from the OnStar system to play through the front speakers when OnStar is active, and mutes the replacement radio. 
• Left and Right Gain Controls: The OS-1 adapter has independent left and right controls that adjust the level of audio coming from the OnStar system.
• LED Indicator: This is an indicator on the OS-1 that lights up when OnStar is active.
• Harnesses: The harnesses allow the OS-1 to be installed in either a Bose or Non-Bose factory system. Refer to the instructions for specific information on wiring configuration for your particular application.
• Inputs/Outputs: On the left side of the adapter, there is an 18-Pin Male Molex plug. On the right side of the adapter, there is a 16-Pin Male Molex plug, and there is a 7" harness with a 9-Pin OS-GM21 connector. Refer to the instructions for specific information on wiring configuration for your particular application.

PAC OS-1 Wiring Interface owner's manual