Circuitron
CF-1 Caboose Flasher

Yellow
Walthers Part # 800-1201, p. 773 Walthers 2012 HO Scale Reference
A scale, $16.95, not currently in stock at Walthers, Expected: Unknown

 
Single rear-facing bulb slowly flashes on and off. Includes CF-1 circuit board, subminiature LED and battery clip. A 9V battery provides about 100 hours of flashing.