Circuitron
FL-2HD Alternating Flasher

Walthers Part # 800-5122, p. 289 Walthers 2012 HO Scale Reference
HO scale, $24.95, currently in stock at Walthers

 
Flashes LEDs or lamps. Connects to Detection Units. Maintains constant flash rate. 1.5 x 3" printed circuit board. Requires 10-18V AC or DC input. 250 ma. output.
 
500 ma. load capacity per side. Adaptable for all scales.