Mike posted one of my pictures in #10, but this is the picture for the TWOLITE system only.
The earlier switch used with the fluted lens headlamps must match and is pictured above in #9. Notice the switch spider and contact plate each has 4 contacts. This has 3 positions, headlamps, off, and parking lamps. Some people change the bulb from a headlamp/parking bulb to a bright/dim headlamps bulb.
The fluted headlamps (3 position switch) was used from the start to February 1929, when the new TWOLITE headlamps with a 4 position switch was introduced.