CAR RADIO HELP AHH 05 chevy trail blazer bose 6 cd stock radio?

my mom has a 05 chevy trail blazer with the stock bose 6 cd changer stero system ... i pulled it out to put an aux wire in for mp3 players or whatever she wants to play....it has a on for aux......but were do i put in the wire to run out ? i thought this was goin to be easy help please!