Hi Roberto,
to use wirings you have to install both Pan 3D view and Wirings plugins. It's highly recommended that you always install the latest version of the plugins, currently Pan 3D view is at 3.7.4 and Wirings at 4.1.1.

If you use SH3D in Italian the help is under Aiuto > Guida disegno impianti.

I strongly recommend to install the Plugin manager first, it helps to manage and keep updated all plugins directly from Sweet Home 3D.