Mach 460 Help

[splogan]

I have a 95 GT vert. I recently installed a new Kenwood in dash receiver. I put in the 5 volt converter so no popping like the unit that came out. I have noticed, the top rear speakers do not work. The subs below do and the fronts all work. I used wiring harness adapters so those should be good. If I move the audio to the front everything still works, including the factory subs by the rear seats. If I shift audio to the rear no sound at all. Could this be a blown amp in the Mach system or crossover in the system. I really don't know much about how the system is laid out to start troubleshooting.