When raido tirns on it displays an error what would it be also need a guide on fuses as cover dont show one

Radio wont turn on neither will aircons or anyother controls there unless radio is on says error if not somtimes wont even turn in to the point it says the error any ideas? and also need a fuse box guide as it dont have one on cover also wanna know whats that brown plug ment togo to as i found where it goes but nothing there to connect

8volts from a battery can and has run my au falcon in accessories mode and has ran my radio before, same situation, but radio doesn’t turn on, replaced fuses 3 times. Is it because of the battery