1997 Pontiac Grand Am battery drains / car won't turn off

Electrical problem
1997 Pontiac Grand Am 4 cyl Automatic 87,000 miles

I have noticed recently that my car sometimes will not fully turn off when I take the key out. The rear defog light stays on. Sometimes while driving the radio and winshield wipers cut out for a few minutes but only occasionally. This problem drain the battery dead 1 month ago and they also replaced something that helps w/ keeping the battery charged.
My new battery was dead again this week and they said it was some lever in the trunk that kept that light on, but the car still has problems where I don't think it is turning off, they said it is not the ignition switch and checked the rest of the electrical system.
Any suggestions on the problem?
Any suggestions on how I can ensure that my car is off besides disconnecting the battery?