I've had another look. The relay is for the dim-dip circuit. Basically it switches when sides are switched via a resistor to the dip beam circuit, supplying about 5.5v at the connector to the dip beam. This explains why the dipped beam comes on (less bright than usual) when sides are selected. When headlamp dipped switch is selected then full 12v goes to the dipped beam (11.3v at the connector). So the dim-dip is a kind of primitive daytime running light set up to give better illumination when sides are selected (a bit strange but hey-ho).
As the n/s works all ok, the fault can only be at the fuse box onwards, as the o/s dip and main has it's own wiring only from there. It is connector B1 at the back of the fusebox, no other connectors on the wiring diagram. Anyhow, for now everything is working, good voltage at the headlamp connection. If it plays up again there are only 2 places to look, 11 something volts at the headlamp connector (or 5.5 if on dim-dip) in which case it must be the spade connector in the headlamp bulb block, or if no voltage there, then the fuse box out to see what's happening at B1.
To be honest, we were in Scotland for 10 days and it was damp and wet most days....can't be the earth as I said, the mainbeam is fine and the earth is shared.
It's surprising that the headlamp circuits go through the column switch with no relays...there is only one relay in the circuit and this is for the dim-dip resistor.
