I'll walk you through the steps I'd take while I'm adding wired (it'll be using an example I've just made up), however you can really do these in any order just as long as it's done properly.
Next head on over to WiredBoxTypeUtility.cs and under the WiredBoxType FromWiredId and inside the...
By latest PlusEMU you mean..? You could of downloaded it from anywhere, however did you even attempt to read the code you was supplied? It says "namespace Plus.Communication.Packets.Incoming.Messenger" so go into your Communication Folder, Packets folder and so on until you reach SendMsgEvent.cs