Headlight Issue

Well, the brights lever is separate from the headlight switch, so that wouldn't be the problem. It sounds more like some kind of intermittent ground problem, with a ground lead to the chassis or a headlight relay with corrosion on the lead. I would trace all the wires associated with the headlights and wiggle them one at a time with the headlights on. Watch for the lights to flicker and you have found the problem.