This is a Surefire Remote Switch known as the Remote Dual Switch 7" Cable, model SR07.
The SR Remote Dual Switch provides remote activation for any SureFire Weapon Light with a switch socket. Two switches-a momentary-on pressure pad switch and a constant-on pushbutton switch-are integrated with a Snap-On clamp for easy attachment to your firearm's Picatinny rail forend. The SR07 has a 7-inch cable which works with most rifle/carbine applications. Fits: Millennium Universal" Classic Universal" Scout Light with socketed tail cap" and X200" X300" and X400 with XT tail cap.
Provides remote momentary-on and constant-on Weapon Light activation
Switch platform clips to Picatinny rail
Weatherproof switches and plug