an adapter for a trailer socket of a trailer coupling for coupling a trailer , wherein the adapter comprises a base body and a primary contact arrangement mounted thereon and comprising a plurality of primary contacts corresponding to a european or german standard , in particular seven primary contacts according to din 1724 or thirteen primary contacts according to iso 11446 , for establishing an electric connection to corresponding socket contacts of the trailer socket . the adapter comprises a secondary contact arrangement mounted on the base body with secondary contacts according to a us american standard , so that a trailer plug corresponding to the us american standard can be electrically connected to the secondary contact arrangement for the power supply of a trailer , the secondary contact arrangement and the primary contact arrangement being connected to one another via an electric connection arrangement .