This happened to me once when I was doing 60 mph down an unlit country lane in pitch darkness. Switched main beam on and all the lights went out. Slammed the brakes on and stopped in the middle of both lanes. Couldn't get the lights to work at all and had to wait for another car to come behind me and use the light from his headlights to get me onto a street lit road. Removed the floor switch the next day and cleaned all the connections and used some electrical grease and it's been ok since then.