I dislike all things wiring, and accordingly, am quite blissfully ignorant on such matters.
So....one of these maybe ??
9438
Trailer Connector - 7-Way European Round To Flat-4 Conversion Plug / Harness
Trailer Wiring Adapter: 7 Way Euro Round To Flat 4 Conversion Plug
(This handy Flat-4 trailer wiring converter is a plug-n-play solution for Rovers with a stock 7-Way European-style trailer connection. Simply plug it in to your stock 7-way connection and the opposite end has a functional flat-4 standard North American connector to rout to your trailer and enables your brake light and turn signal functions.)
9439A
Trailer Wiring Kit - Flat 4
Land Rover Trailer Wiring Kit - Flat 4
(An Atlantic British Exclusive! We've specially-developed these trailer wiring packages for Range Rover Classic, Discovery I and Defender vehicles. These kits seamlessly convert your Rover wiring plug to a standard 'Flat 4' North American spec plug. Our quality harness kits are dependable and cost a fraction of the genuine versions. They feature a rubber plug cap to protect the exterior trailer plug from the elements and easy plug-and-go installation means they can be installed in minutes. Stop and turn functions rated for up to 5 amps. Taillight function rated for up to 6 amps. Complete instructions included.)