1999 Silverado Z71 5.3. 114K miles. Strangest thing, all of the sudden the cab hvac blower motor will come on at a random time and run till it kills the battery. I just put a battery in the truck today as the old battery kept dying and I couldn't figger out why, now I'm not so sure the old battery was bad. drove it about 100 miles and all was fine. parked it and sat there waiting. after about 30 mins the hvac blower came on full speed on its own, with key off and kept running non stop. I had to drop the passenger cover and pull the wire harness to kill the blower motor. if I remove the battery terminals it seems to reset but will still come on at any random time. If anyone happens to know a cause of this I am all ears (or eyes in this case). Thanks for your time and any info is greatly appreciated!