[donv]

The US-style lighter socket is a different size than european. There are "adaptors" available (my original old Escort radar detector came with one) that are really just a hollow tube that goes around the plug to make it thicker. The tube has notches (picture the top of a "castle" chess piece) that allow the side contacts to still touch the sides of the socket but also fills out the plastic tube part elsewhere.

If you can't find one, a few well placed strips or wraps of electrician's tape on the plug should do it for you, just get it to the point that it doesn't wiggle any more but the side contacts can still touch the metal barrell.