Stock Mach 460 Radio questions


I have a 94 mustang with the premium sound system and I'm going to switch it over to a stock 460 system and I have a question about the wiring. In the back of the 460 radio there are 3 places to plug
in the harnesses. Two of them are small sort of squar plugs. 1 is for the radio to amp Harness where
does the other one come from? Does the harness that runs to the rear speakers and amps plug in there.?

Also the amp in front has 3 plugs where do they come from or go to?