Ive got a 1990 chevy truck and i pulled out the radio and equalizer to install a CD player and dont know where to wire it in. there is some kind of box about 10x8x3 inches under the dash and that is where the radio and equalizer plugged into but the harness i got from autozone does not fit this(could be wrong harness). what is the box and do i need to plug into that or pull that out and do something else. I have installed alot of cd players and its usually pretty straight forward but whatever chevy did in this year truck has me confused. point me in the right direction please.