My amp wont work...?

i have a jensen 9412 hu, a sony 1200watt 2chn amp and two 12in subs( sony). ive tested the rca cables and i get a signal, but every time i hook the rca cables up to the amp. the protection light comes on.... also i tested the terminals for the speaker output and for some reason both negative and positive terminals are negative... This occurred on both the old amp.... and a brand new one....