I've got a head lights on and off issue too at the moment on mine. I'm fairly sure that the issue is from water ingress to the fuse box. I've had a few times where there has been lots of water on the fuse box, so I think it'll have buggered a relay or two and they are rusty and intermittant.

I'd start with the relays which are on top of the fuse box. You need to undo the screws which are on the fuse pannel and then pull the fuse box down to get to the relays.

I'll dig out a haynes manual at some point and work out which relay its likely to be and update this if i remember.

JAmes.