Audio Systems: Mustang Mach 460 Sound System, rear parcel shelf, mustang mach

Question
Hi,
I just bought a 97 Mustang with the Mach 460 system.  With the volume cranked full throttle all I can hear is minimal sound.  I believe it is only coming through the front 2 window tweeters and back 2 tweeters.  I have tested the radio unit and that is fine.  I have checked all connections and they appear fine.  Any ideas?
Thanks

Answer
The amps for that system live under the rear parcel shelf, and it's a big job to remove the assembly. I would check ALL fuses  in both fuseboxes before doing anything else. The previous owner may have had the amps bypassed with bypass jumpers, and when he put his OEM headunit back in to sell the car, did not put the amps back to original. The amps are quite large, and silver If I remember correctly.