I have seen what appear to be the typical 1917-27 side lamps with both the clear front lens and a smaller side red lens. Can someone shed some light on the use of the one with the red lens?
That is a taillight for the non-starter cars starting around mid-1923.
The red lens faces the rear and the clear lens shines on the license plate.
As Daniel's lamps have a large clear lens in front and a small red lens on the side I believe they are cowl lamps with the small red lens serving as a side marker.
That was my first though, but the lens is too small. I have a tail lamp and the large red lens is in front (or rear) and the smaller clear lens is on the right as you face the car from the rear. The side lamps I saw had red lenses on the outside of the lamp with the large clear lens in front. The lamps are not interchangeable, as one is for the left and the other right side with the small red lens facing outward towards the side of the car.
If you look on the rear side it will say Ford-O it mounts from the side opposite the small lens. This is the non-starter Ford rear tail lamp adopted in 1925-27.
A taillight is not a side light! Also, note that the mounting stud is on the side of the lamp, and not the back.