I don't have a clue what that is supposed to be for.
First I'd check owner/operator manual or ask dealer what application that is for. If it's supposed to be for tail,stop and turn signals plus brakes,I'd either cut wires and run them to a common 7 way or buy male part from dealer then go to regular 7 way. Factory or dealer put it there,they should be able to furnish mating part.