Headlight problem

Supreme bus, 2000, 400,000
I have a problem with the headlights flashing, I changed the headlight switch. It worked for 20 minutes then they started flashing again. The turn signal switch was replaced about a month ago. I started tracing and checking the headlight wiring before I went home. I believe it might be a bad ground somewhere in the wiring. Does anyone know. Did I miss something. Actually I do hope that I missed something if not i'm going to upside down on my head for hours tracing wires