Wiring diagram for a 13 pin tow bar socket and plug many caravans built after 2008 have the new 13 pin connector for the electrical connections to the car. Here is a picture gallery about euro 13 pin plug wiring diagram complete with the description of the image, please find the image you need. This is an extension of the 7 pin flat.
All you'd be doing is wiring the 12N pins in parallel with pins 1-7 on the 13-pin. If the 12N socket has no fog light cutout switch, then the fog light may not be switched off if you connect a trailer up via the 12N.