I wonder if you put a screw through a wire somewhere causing a short. I have always just cut the ground wire from the motor and then spliced into it with the new therefore using the same ground. I do not know which of the few blower motor replacment methods you used. I also do not know that much about AC since none of my as systems has ever worked. Are you sure that the switch is all of the way off? Turn if counter-clockwise hard to make sure it is off. Maybe the switch is not installed correctly thus making it impossible to turn off. Maybe you have crossed wires at the switch.
Are you sure your battery and alternator is good? If you ran your battery down when you were working on the car the car might have enough juice to run until you turn on the lights.
What happens after the car dies? Are the headlights on at full power? Can you start the car with the headlights on? Does it turn over?