Did you already re-wire everything ? Well you should have read the whole instructable first.
You have to thread the wires for the solar panel through the lid of the tin first. Then you can play games with hot lead.
Put some tape (Gaff, electrical, whatever) down on on the lid to insulate the solar panel's contacts from the metal of the tin. Then glue the panel to the lid of the tin, I used double-sided tape for this.