eh...put your amp back in would help! if you have a GTS, all the sound is from the stock amp. the radio itself is not powered...
now, if this is an aftermarket amp. it's prbably the main power for all of your speakers, 4 channel perhaps? check the amp cable fuse, as well as the fuse on the amp itself. instead of having me guessing over here, why don't you explain what you have???