Audio Systems: Mustang Mach 460 Sound System, channel amp, mustang mach

Question
I just bought a 1997 Mustang GT Convertible with the 460 sound system.  Everything seems to work on the left side but nothing works on the right side.  If I set the balance all the way to the right there is no sound at all.  I bought another head from a junkyard that "supposedly" was tested and it did the same thing.  Any thoughts?

Answer
I'm pretty sure there is an external power amp supplying audio power to the speakers. Rear amps can be found as shown here:

http://www.flemworld.com/Mach460/Mach.html

Right channel amp is out?  Wiring gone open circuit?  Do you know how to swap the channels?  Take the audio cables from the output of the head to the amp and just reverse them; it will tell you if the amp is working.  Or, at the output of the amp reverse the right and left speaker wires.