Trigger switch problema!?

[Spa]

So, Just recently my friend took apart his G36C to put a new spring in and inconviently enough, the wiring for the trigger box came out.

So we put it back together and now the gun will only shoot in semi auto even in full auto mode..

Question is, how does semi and full auto work in an AEG? and how can this problem be fixed? or what is there to look out for to avoid this problem.

Thanks for the help.