Switch could be bad or wiring could be ripped on the steering column. The switch is just a momentary switch. It only closes when pressed but the computer senses this. Any way there are two wires that feed down the handle down the top of the steering column and around it toward the base and connect to a small, im talking small connector.
Best way to test this switch is to get to the plug and get an ohmmeter and check for continuity whens its pressed.
If it turns out to be your switch a good upgrade to do is a Crown Vic/Lincoln Shift handle like I did. Its factory chrome. Here is my how to:
http://www.ranger forums .com/showthread.php?t=118753
It also shows the routing of the wires.