Problem with heating system!

I started having this problem with my heating system. Sometimes when I start my car, i can't turn on the heat. I'll switch it from 0 to 4 and nothing works. Sometimes I just turn the car off and back on and it'll start; other times all it takes is a bump in the road. I'm guessing it's a loose connection. Any ideas where to look or anything else it could be? Anyone had this problem before??
 
Resistor box by the blower or any of wires between that and the actual switch. Maybe even the actual power lead to the blower too. Should all be behind the glove box.
 
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