Postwar 154

The #1 terminal is common and usually goes to the central rail. Terminals 2 and 3 each light one of the red lamps. This is designed to work with the 154C track clip. I do not know if there is any thing equivalent for Fastrack.  You could get a electronic crossing lamp flasher.  Dallee makes one.  It alternately flashes the lights. There is a single wire for turning the flashing unit on with power from the track. 

What he said.  Dallee 367.  Link has easy to follow wiring instructions.

There are other suppliers of flasher modules as well - seem to be in the $20-$30 range.  If you want to dig deeper, search OGR for something like "154 flasher" and you will find dozens of ideas from DIY circuits (requires soldering) for a couple bucks to more complex (expensive) flashers such as with accompanying bell sound.