turn signal on back passenger side dont work when headlights are on works fine when headlights are off when i hit the turn signal when the headlights are on the fog lamps i think thats what they are comes on and the turn signal flasher goes fast

 

Check the ground wire to that light. Trace the black wire to where it connects to the frame. Loosen the screw holding it a little and wiggle the connector to break up any corrosion, then re-tighten the screw. That should do it.