I would check the accessories fuses first to make sure they are all good, then you will have to disconnected, and get a multimeter to check the wires, here is how it works, one wire by applying positive to it should turn on accessories, another wire by applying positive should turn on the system, and another one should turn on the engine, the accessories may be more than one wire, the ignition should supply power to the wires, you need to find the diagram for the wires to see which wires turns on accessories, if you apply 12v to the accessories and it works well then is the switch that may have a problem, if you apply 12v to accessories and it doesn't work I would check the fuses again to make sure all of them work, if nothing else works well one possibility is a wire is bad somewhere in the car.