I have an '87 F-250 that has turn signal problems. I turn my turn signal on as if I were to turn left and I notice that my driver's side front turn signal is not flashing but the driver's side rear tail light turn signal flashes just fine. Both turn signals on the passenger side work. I find it a little odd that the rear flashes but not the front. It's not the bulbs because my running lights work, so I'm kind of confused as to where to look first, any thoughts?