The only thing I can think of right now is that when reassebling one of the end plug pins has to go under the wire of the safety catch(can't remember which one,I think the rear pin). But it can be lifted with a small screw driver so the pin can go under it and through the plug.HTH,Mulby.
When reinstalling the trigger unit, its advisable to use a slave pin in the rear hole. Make yourself a pin that is the same diameter, but only long enough to go through the trigger housing, and still slip into the receiver tube. That way, you can get the safety spring thing into proper place before putting the trigger unit back in the gun. I got this piece of advice from, I believe, Lewis Reinhold, and it saved lots of headaches during re-assembly.