A couple of things nobody mentioned.

On the SP, they had lower quadrant semaphore signals, that would only show 2 indications per blade. In places like the Siskiyous you would report the lite out but they never were in a hurry to replace it. You could still see the indication the signal displayed by the position of the blades so you didn't have to stop like an H Head and such. So the maintainers were not in a hurry to get a motor car out in the snow and fix it. The signal up by Tunnel 14 & 15 was usually out for months.

The other is that some signals have to have a bulb where the filament has to be positioned straight across the lens. That takes a special base and bulb to go in it.

Most signals were 10 volt DC. The banner motor in a Griswold or the magnets, clutch, etc. in a wig-wag. Most of the TC batteries were around 3 to 6 volt DC, depending on the design, etc. They needed 110 AC to run the power supplies to keep everything charged.

General Electric has a whole catalog with nothing but bulbs for railroad signals and equipment. They even sell 74 V DC sealed beam lights for your locomotive parked around back. You name the voltage, wattage, the base, etc., they have it.

Nudge