I have a 03 GT with the JBL 8 speaker system. I wanna hook up a sub, how can i do it? i tryed splicing it into the rear speaker but it didnt work. The sub was recieving power but nothing was coming out. I hooked up another speaker and that worked, but the sub wouldnt. So thinking that the stock system wasnt pumping out enough watts i went out and got an amp. The amp, however, cant be hooked up to the stock head unit because it doesnt have input/output plugs. Does anyone have an idea. I can go get a new head unit but i wanted it done for this weekend. please help.