I have a 92 camry that has the Anti-theft radio/cassette system installed. The radio quit working and I have checked all of the fuses and relays and all seem to be okay. Dome light still works. Cig lighter still works. When I check the plug that goes into the back of the radio I am not getting any 12 volt readings. Should I be getting a 12 volt reading on specific wires? Also, I traced the wiring harness from the radio to a box located under the passenger seat. What is this box? Is it an amplifier for the radio? If so, what are the chances of this having gone bad?

I know there a lot of questions, but I just want to get the radio working again. Any suggestions would be greatly appreciated.