[alantf]

Yes, the earth goes back to the battery, but it picks up all the other earths on the way, so there are lots of connectors to check. The first connector goes to the front indicators, so, if these are working, the earth should be ok right back to the battery. The pass switch feeds a contact in the light switch, so power is getting to the switch block (to a separate contact), then to the headlight. This shows that live and earth are both ok in the headlight. I'd still put my money on it being a problem with the other contacts in the switch.