I went back round today for a other crack at it.
Once again, the booze flowed.
Anyway, I retested the power at the switch, and couldn't get a reading even with the main headlight switch on. So I pulled column shroud, and had another play.
I stripped the switch apat, and cleaned the contacts with wet and dry. seems to have fixed it. Although the screw that holds the contact assembly has stripped out the white plastic of the switch body.