Had a question on the lighting arrangement on UP's FEF locomotives post WWII. The red light, above the headlight on the front of the engine, was illuminated when the locomotive was in reverse.
Only if the Engineer turned it on, i.e. that Mars Signal Light ONLY comes on when the air brakes go into emergency.
That light could also function as a MARS light. I'm assuming that the light was only oscillating in an emergency stop situation or for some other emergency situation?
Yes. However, the Engineer could, and did, turn it on when stopped in a multi-track depot, in order to alert oncoming trains to NOT pass the oscillating red light (by operating rules).
Otherwise it was only illuminated steady on in reverse.
Again, not necessarily, as the Engineer would have to turn it on. When operating in reverse, the class lights would be changed to "red", and turned on.
There is also a red light above the back up light on the rear of the tender. When would that red light be illuminated?
When/if the locomotive was running light, or as a rear end helper, the rear red light would be turned on, just like red marker lamps on the rear of a caboose or passenger car.
Was that red light a rear marker when the locomotive was running light or was it illuminated anytime the locomotive was in motion?
As answered above, the red light on the rear of the tender was manually controlled by the Engineer, and would generally be turned on only when running light, or as a helper on the rear of a train.
