85Rx007

Ok, I'm sure this is covered somewhere but I cannot find it anywhere using the search. I have a quick question on how this is supposed to work. I talked to 2 seperate shops today about removal of the stock stereo and speakers and replacing them with new ones. They state that there is an amplifier that is located somewhere in the vehicle, one says behind the dash, the other says under one of the seats. I tore apart my dash, and took a peek under the seat, I don't see squat. I am trying to make the wiring harness match up and fit but it just won't. Is there a "FB Stereo Installation for Dummies" out there? Please advise. Thanks in advance.