If you are on Windows:
Go to "C:\[USER]\eTeks\Sweet Home 3D" with your file manager. There should be a folder for the plugins. Delete the wirings sh3p file and you can start Sweet Home 3D again. Now first install the Pan3DView plugin before you reinstall the wiring plugin.
I suggest that you install the Plugin Manager as mentioned in the post right before yours and use that to install other plugins.
On Linux the plugin directory is /home/[USER]/.eteks/sweethome3d/plugins. That is a hidden directory so don't forget to switch your view in the file manager to view hidden files. (Notice the . before 'eteks', hidden files/directories start with a point on Linux.)