I've got a '76 Chevy 3/4 ton pickup with an aggravating problem; the defroster fan will intermittently fail to work. When it does work it functions just fine, but then for some reason when I shut the ignition off and then restart it, it wont turn on at all. Sometimes it will "wake up" when I hit a bump or slam the door. Does the fan motor have a ground wire that might be loose? Where is the fan motor itself located? I need some way to keep the windshield defrosted, even if it involves jury-rigging some sort of bypass switch. Any advice would be appreciated.