Here are diagrams of the wiring layouts for a 12N (standard British towing plug/socket),

12S (standard British caravan electrics plug socket) and 13 pin DIN plug and socket 

(the continental style wiring which combines all the towing electics functions into one device).

PLEASE NOTE THAT THESE DRAWINGS SHOW THE PINS LAYOUTS ON THE FRONT

OF THE PLUG AND SOCKETS. THE LAYOUT OF TERMINALS, LOOKING FROM THE

BACK OF THE PLUG OR SOCKET IS, OF COURSE, A MIRROR IMAGE.

Terminal 4 on the 12s unit is Green; Postive, direct from battery.

Terminal 4 on the 12N unit is Green, R/H indicator

Terminal 9 on the DIN unit is Green, ornage or purple, continuous 12v supply.