Headlights come and go

Hey guys. I noticed something today when I was driving in the dark. My headlights come and go. For the most part they stay on, but then all of a sudden the will flicker and or go out. So I just pulled the knob on the switch in and out and they come back on. Never noticed this problem before, I washed the car recently, all I can think of.

Car is a 1970 Duster. I'm gonna look into it, but thought I just toss it out there if you have any ideas. Probably bad ground somewhere, just seem odd that they will go right back on if I pull the knob on the switch in and out again.