Fuses for the CR-712 are on the back of the unit. They are the blade style 3 amp fuses, but I doubt that they are your problem. I would suspect either the wiring or the CR-712. Check for constant power on the green wire, and switched power on the blue wire. If these are hot and the unit is grounded the radio should light up. The radio does not have a ground lead in the harness. It is bolted to the nut on the back of the radio. The four loose wires are probably your rear speaker wires. The CR-712 does not have rear speaker outputs. You need a power amp to hook up rear speakers. The only power amps that can be easily hooked up to Volvo radios is volvo brand, that plug into the din plug on the back.