The floor-mounted dip-switch used until 1970.

From 1970 a column switch was used. This from a UK 1973 model, showing the switch in the 'main beam' position, 'dip' and 'flash' contacts both open:

Showing the switch in the 'dip beam' position, 'main' and 'flash' contacts open:

Showing the switch in the 'flash' position, dipped beam contact still closed (but the spring contact pushed further than before), 'main' contact still open:

Showing the switch in the 'dip beam' position with the contacts labelled as to which colour wire goes where:

A general view showing the plastic springs (and indicator/turn-signal auto-cancel fingers) on the switch body. The 'Dip'/'Main' snap-action spring gives the positive switching action between dip and main positions. The 'Flash' spring gives a positive return to 'Dip' from 'Flash':

Switch in the 'main beam' position, headlamp wire and main beam contacts closed:

Switch in the 'dipped beam' position, headlamp wire contact between main and flash:

Switch in the 'flash' position, headlamp wire and flash contacts closed:

77 and later: Unlike the indicator contacts the dip switch contacts can be accessed directly (see here for info on the horn button). 'A' are two fixed contacts having a 12v supply when the main lighting switch is on headlights. 'B' is the dipped beam contact clear of 'A'. 'C' is the main beam contact moved up to 'A' to light the main beams:

The dipped beam contact 'B' is moved down onto 'A' to light the dipped beams, 'C' is clear of 'A' to extinguish the main beams:

'B' against 'A' so dipped beams are lit if the main lighting switch is on headlights, and the main beam contact 'C' has moved down onto the fixed 'flash' contact 'D' carrying fused 12v from the fusebox to light the main beams irrespective of whether the headlights are on or off: