I just bought a used Sony HU and was installing it today with a friend and couldn't get it to power up. While I was checking the fuses I told my friend to see if the unit would power up by running the hot and ground wires directly to the car battery, he accidently put the hot wire on the negative battery post and the ground wire on the positive battery post and got a spark. The unit does not power up now and I don't know if I bought a broken HU, if he blew a fuse or just destroyed it(it doesn't smell burnt). Can anyone out there help me figure this out???? Any help would be appreciated!!!