I believe that the upper headlight was built a single-bulb lamp that rotated in a circle. Later, the two-bulb "figure-8" oscilating came late in the 50s-early 60s. The smaller sealed beam headlights didn't come out until the 1958 line of automobiles.
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Why did Southern Pacific replaced the single bulb on the upper nose of the GS4s with the twin sealed beam type .is it true that SP didn't like the design.