im going to assume he is referring to the auto sear. sits above and behind the trigger group, just above the selector switch. that "wire" thats blocking the pin is part of the auto sear spring. at the end of the spring it is bent inwards to act as a lock for the pin. you kinda just have to line up the pin with the hole and hit it with a mallet to push the pin through. there should be a slot cut out on the pin for that section of the spring to sit into.
this is a RS auto sear. the airsoft version should only have one cut out, on one side.
