Seven-pin wiring schematics for trailers are available at RVBasics.com, Etrailer.com and CountryTrailer.com, as of 2015. A seven-pin diagram for Australian trailers is available at Camptrailers.org, and a diagram for U.K. trailers is available at Towingandtrailers.co.uk.
RV Basics provides a diagram that describes the color, gage and circuit function of each of the seven pins. Etrailer.com's schematic gives descriptions and diagrams of multiple connections. Countrytrailer.com provides a schematic that gives the post, purpose and wire color for standard seven-way RV plug wiring.
Camptrailers.org has diagrams and photographs of seven-pin sockets and plugs. The diagrams describe the location and function of each pin. The schematic also includes diagrams for six-pin connections.