For those experimenters among you who would like to make their own alternate-flashing lamp system, there is a posting on the EAA CH. 170 web-sit that shows the schematic of system that can be made for about $10-$15. It has the advantage that because of the way it turns the bulbs on through a current-limiting method, it adds much life to the bulbs. My 50W halogen bulbs have over 300 hours and they are on whenever the master is on. As presented, it is meant to be a warning flasher as well as an in-flight recognition system, and is made to be on whenever the master is on. By the addition of a 3P3T switch it can be made to be ON-OFF-ALTERNATING.