Replacing 2000 Suburban factory radio
I have a 2000 Chevy Suburban with a Delco factory radio (model 15764358). As far as I can tell it is not an RDS radio. The car does have On-Star.
The radio has two connectors - The 21-pin connector (power, speakers, mute, etc) and an 18-pin connector. I believe the 18-pin connector provides the interface for communications with On-Star and the rear audio controls. This unit does not control chimes.
I am replacing the factory radio with a Pioneer unit (DVH-P5000MP). I was under the impression that I only needed to make connections to the 21-pin connector if I didn't care about On-Star or the other secondary functions. Unfortunately, that doesn't seem to be the case. When the Pioneer unit is connected to the 21-pin connector it powers up normally and seems fine, but nothing comes out the speakers.
After some testing I've discovered the 18-pin connector must be connected as well in order to hear anything through the speakers. I did this by reconnecting the factory head unit and connecting/removing the 18-pin connector. When the 18-pin connector is attached the factory unit plays through the speakers, but when disconnected nothing comes out.
I'm making the assumption, perhaps erroneously, that the On-Star system somehow captures the links to the speakers (perhaps through a secondary amp) when the 18-pin connector is not attached. I have not been able to find any info about the pinouts on the 18-pin connector.
What is the best way to bypass/incorporate the 18-pin connector requirement? I don't care about On-Star and would have no problems with disconnecting it if I knew how and that was the answer. I've also seen info about the PAC OS2 connector and would go that route if that is the answer.
Any help would be greatly appreciated.