How can you change an ignition switch for a 90 Mazda miata?

Take off the two pieces of plastic that round the steering wheel (4 or 5) screws, and look on the opposite side of the key hole, there will be a yellow end (plastic and contacts) attached to the metallic part. unplug the harness that connects that end, and look for a screw on the top of that yellow part (note: the yellow part is your switch). Take that crew (self tapping) off and then just pull gently your switch, done.