Audio Systems: car radio, gmc dealer, gmc envoy

Question
i bought a 2003 gmc envoy and it was missing the radio.the person who owned before had a big box with aftermarket speakers in the back of the truck and changed the door speakers. i nstalled a factory radio but i dont get any audio coming out to the speakers.the radio is working because i connect a speaker right behind the radio harness and audio comes out.somebody told me that some cars come with an external amplyfier but i cant find it.i dont know if this truck came with a bose system.  thank you  

Answer
Luis,
You should ask your local GMC dealer for a print out of all the options for the sound system for your vehicle by using the VIN number. This info will tell you every thing about the sound system and if an amp was installed. You might also ask for a wiring diagram for your sound system.

TOM,
T&D ELECTRONICS
tdeser@zoominternet.net