1999 chevy blazer, factory ac delco cd/tape player, no sound coming from rear 2 speakers, want to check amp but cant where is it located?

I am working off of a 2002 wiring diagram here. It shows an audio controller behind the B pillar and also shows an amp behind left center of trim panel. This only applies if you have subwoofers from the looks of the diagram. Again, this is a 2002 and it may have changed.

Steve

thanks for the info!