The two parts of the Wii zapper that should open/remove for the nun-chuck wires to go in are very difficult to get into. The back one that locks the nun-chuck in place seems very stiff and hard to open, and the sliding case that hides the wires doesn't seem to open all the way for the wires to be put in. I imagine that when it is installed it would work as it's meant to, but as of yet I haven't reached this stage.
Update: After upwards of half an hour wrestling with the clip at the back I managed to get it open. It involved me having to take the selected area off with a screwdriver and having to widen the (previously too small) gap for the clip to go through with a file. The other compartment came off easier, but still took far longer than it should.
I must say I'm disappointed at the amount of hassle it's taken just to undo two clips, but I guess at low costs you have to expect lower quality.
Now that that's being done however I'm ready to use it to play with and am looking forward to it.