Good chance the plastic housing on the switch that the tabs for the back part of the switch lock in to is cracked. This allows partial contact within the switch in some switch positions. Call your nearest dealer and ask them to run your VIN and see if recall 94 applys to your car. If it applys and has not been done, they will replace your switch free of charge. If not, you will need to replace it at your own expense. Don't quote me but I believe the switch runs around $60-70. It is easy to replace. Pry the knob off with a screwdriver, then grab the shaft with a pair of pliers and pull. The switch housing will come out of the dash, and the back panel on the switch will probably break off the rest of the retainers. Now fish the remaining bits out, and unplug the wiring, plug in the new switch, and press it home