So sorry MELGAR and Chris - as with so much lately, I missed your replies.
MELGAR; I had a similar thought, but I don’t think there is a missing receptacle - here is a close up picture. As you can see, the LED is fairly large and wouldn’t fit into much of anything in that location. In addition, it can’t be pulled back into the body of the unit.
Chris; the light is always on, regardless of the direction of the unit. The A units have a light above the rear doors, and the B unit has one above the front and rear doors. And a question... when you say “hostler’s light” - is that the proper term for, what I call, the backup light???
The mystery continues
Thanks.