93 bravada ignition switch???

hey guys just moved back to cincy last week and already working on the kids cars.This problem came about last fall around the time we replaced the starter(cant remember if before or after) here goes.93 bravada 4.3,smartrac,tilt,cruise,automatic.when its been raining out when my son tries to shut the car off it continues to run,not deiseling but running,sometimes the abs light in the dash stays on and the parking lights stay on.Iwas just at the car and if i work the key,going from off to acc. to run i can get the abs light to go off(sometimes).The only way to get it to shut off is to disconnect the battery.HELP!!!!

Whatcha know Daddyo?
Sounds like the ignition switch on the steering column under the dash is going bad. Here's a pic of what you're dealing with.
http://www.autozone.com/servlet/UiBroker?ForwardPage=/az/cds/en_us/0900823d/80/05/00/ee/0900823d800500ee.jsp