85 BMW 535i help replacing ignition swith

when turning the key my ignition lights comes on fine.but if i press to start the car nothing happen. my starter n connections are good need some help in replacing the switch,i like also to know which wires to cross to start the car.ty

Could be a starter solenoid...do you hear a "click" when you turn it to the on postion? If not that could be it.