Suburban 2002 onstar mute

Hello everyone I have searched but have not found the answer. I would like to know how the onstar in a 2002 Suburban mutes the stock radio. The radio is a non RDS and has both a 21 pin and 9 pin plug. I have found harnesses and instruction for the rds radios (03 and up in GM trucks) but not for the non rds. I would like to use the same mute trigger for other audio sources(e.g., gps). Any help would greatly be appreciated, thank you.

The Onstar uses a data message through a wire to tell the factory radio to mute the front speakers and select the auxillary input audio from the Onstar and direct it to the speakers. I don't think you are going to be able to do it this way.sparky