In the game there are normal coupler types available, however none of them seem to be able to connect to the drivetrain of the vehicle. The idea here is to add the coupler, which would be able to transfer power from either shaft, transfer box, or transmission of the vehicle to the drivetrain of the attached trailer. Here's example from real life vehicle, which has such coupler: In this example the main vehicle can transfer the power through the transfer case, into the fifth wheel and through the kingpin to trailer's own differentials through its driveshaft.
