Hi Joe - encountered this many years ago and came up with the following.
Dim Lights Bright Lights
When I first started restoring Chevrolet instrument panels, as usual, I obtained the best NOS speedometer and instrument faces to replicate. My first speedometer face just happened to be a “Bright Light” face and several old panels I obtained were all the same. Lately though the ones I have been obtaining have a “Dim Light” face. Of course I didn’t discover this immediately until I was comparing instrument serial numbers and found that I had two different numbers for the speedometer face. Shock, horror, where did this “Dim Light” come from and what was its history.
I consulted one of my guru contacts who told me the following. Prior to about 1938 there was basically no beam indication in a speedometer. In about that year Pontiac and Chevrolet built in a low beam indicator and that was described on the speedometer face. In the late 1940s, apparently after many complaints from army drivers, the wiring was changed to allow a high beam indication and that was reflected on the new speedometer face. I do not doubt the veracity of this story but would be interested for any corroboration. As an aside apparently the British were high beam indicators right from the start.
BTW your replacement switch and plate are en-route.
Bob