Headlamp issue on Yamaha YBR125

[FraserG]

It comes and goes now. It appears to be a dodgy earth wire, as when the light isn't work, both low and high beam are receiving voltages but the earth isn't returning anything. I've cleaned the earth connectors and now it comes on. Sometimes it doesn't, but a short sharp smack brings it back. Which is handy, given the fog we've had today!
During the winter (when I get my new house with a nice garage) I'll strip the wiring and see if I can do something to the earth.