7 Way Wiring Diagrams:
There are two wiring codes for different types of 7-pole plug and socket sets.
Most RV's use the RV wiring code for the type plug/socket that has 6 flat contacts
surrounding a center round pin. Semi's and commercial trailers use the
ASME (American Society of Mechanical Engineers)
type 7-pole plug sets. These plugs have 6 round contacts surrounding a center round
Commercial Truck and TrailerWiring Diagram.
Light Duty Non Commercial Truck, Fifth Wheel and Travel Trailer Wiring Diagram.
Note: the ways to convert from 7-Pin Commercial Plug to the 7-Blade Light Duty Plug is covered in
This drawing from Mark Bruss shows the relationship of the 7-round to 7-flat plugs and how only
three wires are common.
6 Way & 4 Way Wiring Diagrams
BTW, the wire colors on your truck or trailer could vary from the colors
shown in the diagrams.
Otts Friction Supply
on eBay is a good source for
ASME Commercial Sockets, Plugs, Rubber Boots
and other HDT related items.