When I turn on headlights I get no tail lights. The brake light and turn lights work, after replacing their fuse. What appears to have happened is that the trailer plug on the truck came loose and shorted. All other fuses for the truck are good, and the tail lights bulbs are good. I checked the plug with a voltmeter and got nothing. Is there another fuse somewhere or relay that could be bad? I have no wiring diagram/schematic, Help!