im not sure how you have the kit or how its set up. but its really simple,
you need a feed line off the bottle to the solenoid and then another feed line off the solenoid to the elbow.
2 wires off the solenoid, power and ground. go to radio shack and buy a momentary switch. not the on off one, the one that you can hold down and when you let off it releases.
wire that to the solenoid and then ground to the battery. turn the bottle on and when you want to use it then just hold down the switch. dont leave the bottle on for long periods or time though.
heres an example how its wired up when buying the old nx kit. small solenoid btw
Google Image Result for http://www.volkswagendatabase.com/images_articles/rd_nitro01.jpg