ISO radio connections?

My kenwood KDC-3024 is installed in my 1997 VW caravelle through the ISO blocks A & B. The battery and ignition cables are crossed over as instructed in the manual. But my rear speakers are mute. Front speakers are fine. If I fade to the rear the sound goes completely. Could the crossed over power and ignition be the problem, or is the radio not powering the rear speakers due to a fault in the radio?

John Birch
April 2007