Well, I'm giving up at this point. Sound coming through the door speakers is really good & strong. Various wiring swaps I tried didn't ever produce any sound from the subwoofers. I'll take a coupe of days to study the wiring diagrams (by the way, the wiring diagram in the 2007 Shop Manual is somewhat different than the one posted earlier) & maybe give it another shot later on. ala_xfire - Thanks for your help.