2007 F350, 97K miles. I replaced the dash switch thinking it shorted out. Anyhow, every now and again, the headlights turn off. The fog lights stay on, marker lights, dash lights......EVERYTHING EXCEPT HEADLIGHTS stay on. Then they just turn back one. I am GUESSING it is a ground but does anyone know where and if there is a ground wire just for the headlights?

 

I'd ask for someone to post a schematic showing the wiring for the lights so you can trace it back to the point of commonality between both lamps.

I'd have to figure each bulb is grounded right at the fixture, and of course the likelihood of them both failing at the same time is about zero.

I'd be thinking maybe corrosion around or beneath the fuse block or something similar, like a relay. I'd doubt a fuse problem because they don't self-heal. Still corrosion at one of the brackets that hold the fuse might be suspect?