2004 f650 lighting wiring

I'm looking for a wiring diagram for a 2004 f650. rear passenger brake and blinker stopped working. there is a 3 wire plug 1 wire is for running lights one is for the rear driver side blinker and brake and the third shows voltage when its unplugged for the rear passenger brake and blinker but as soon as you connect the lights or a light tester the voltage disappears. any thoughts?