scanner problem..

i just recently tried to install a led-scanner into my car, there are three wires to hook up, one for pos. on battery... one for neg. on battery... and one for a device that is active while car is shut off... the directions said to connect wire to radio fuse, but all that did was blow the fuse :banghead:.

so if u have any idea on how to finish hooking this thing up , please help me...