Problems with car subs? i need help!!!?

hi, okay i have wired up subs in my own car previously to this, but my friend and i were wiring up subs in his ford ranger, but after hooking everything up, we turned the radio on and there was nothing coming from the sub, so we hoocked the sub into my car( i already have subs) and it worked so the sub itself is fine, but then when we were bord we put a cd in and the bass was working in the ranger but there is no sound coming from the car speakers! (so the subs dont work when we are listening to the radio, but the car speakers dont work when we listen to a cd) so we dont know if we wired something wrong with the amp/sub or is there is a wiring problem in the radio! any ideas or awnsers will be greatfully apreciated! thanks