Kit requires you solder. Takes little over 5 minutes to install. only difference between variable kit and black ops kit is that variable kit has a variable resistor so you can alter fire rate. hold down button and trigger to activate rapid fire.

left wire is negative right wire is positive. in kit wires will be marked

C pin of transistor goes to middle of three pins for trigger(top). E pin goes right below(top). resistor goes to switch(middle). switch goes to trigger wire (bottom)

done