Starter Engaging

[Leonard1]

I originally posted this at chevytalk:

My brother has an '01 Tahoe, and the starter engages at will. It started last weekend when he returned home, and put the car in park. The starter engaged and continued to run, even after turning off the key (which did kill the motor). He had to disconnect the battery to get it to stop turning over. This went on for a couple of days, and he just put it in Neutral and turned it off with no problems. Now it will engage the starter at any time. I think there's a short somewhere, but he can't seem to find one. Any ideas?