1999 Pontiac Grand Prix Blower motor problem

The blower motor will kick on at anytime driving down the road when the controls are set to off. You have to discconect the battery cable to get it to shut off. It will even stay on when the car is turned off. Once you get it to go off it will stay off unless to things happen. One you turn it on then it won't go off unless you disconect the battery cable. Or two it just decides to come on all by itself without messing with the controls. I had to pull the ignition switch power supply to keep it from coming on at all. Atleast the wires where lableled ignition control or something of that nature I just know that it keeps it from coming on at all. What could it be I been told it could be the HVAC Switch or the ignition switch. I am smart enough to know there is a short somewhere but where do I start looking for the root of the problem. Thanks Rocky