This is page is included only because 5 or 7 core trailer cable is the best way to carry the wiring of several components from one end of the car to the other.  The diagram below is the NZ standard wiring for a flat trailer plug/socket, even though the colours conflict with the BSI (British) standard wiring colour codes for cars.  Note that this is the trailer wiring and has no relationship whatever to the tow vehicle's wiring, which will be different from make to make, country to country.