you can pull a fuse out and do what WiLL wrote to see if it's blown. testing with a battery charger is clasic way on the black market to make sure you don't get rip off. all you do is hook the yellow and red wires to the + clamp of the charger and the black wire to the - clamp of the charger, and 1 speaker up to any of the speaker wires. you then slap in a cd and make sure every thing works