Silly question, but are you checking the circuit when it's working, or when there is no power to the headlights? It should be pretty simple to diagnose when they're not working. Turn them on, if they don't work, start checking for power and ground at the harness connections. Start at the lights themselves and move back. Makes sure you are checking power and ground at each spot. Eventually, you'll come to a place that doesn't have one or the other. I suspect its the switch itself, whether or not the contacts were cleaned, it could just be wearing out. But if you follow the circuits path, you will find the problem. Just make sure it's not working when you trouble shoot!