Device for the towing vehicle-trailer connection, comprising: - a base body associable with a trailer and wherein is defined at least a first female coupling, provided with a control line connectable to the braking system of the trailer, and at least a second female coupling, provided with at least an additional line which acts on the parking brake of the trailer and provided with at least a by-pass line communicating with an unloading tank; - at least a first and a second male couplings (12, 13) associable with a towing vehicle of the trailer and connectable to the relative braking system, where said first and second male couplings (12, 13) are connectable to valves able to send to the same, respectively, a working fluid at a first and at a second pressure and are insertable, respectively within said first and second female couplings (3, 6); where said second male coupling defines a first channel for the transit of a working fluid and has a first closing element of said first transit channel movable between an opening configuration and a closing configuration, - valve means able to put in communication and isolate between them said additional line with said by-pass line, respectively, as a result of the exit and the insertion of said male couplings (12, 13) from the relative female couplings (3, 6); and characterized by the fact that said valve means comprise a first tubular element movable in a sliding manner within said second female coupling between a release configuration, wherein said additional line and said by-pass line are mutually communicating, and a fastening configuration, wherein said additional line and said by-pass line are mutually isolated, a second tubular element inserted in a sliding manner within said first tubular element and defining a second channel for the transit of the working fluid, there being provided a second closing element of the second channel itself, said second tubular element being movable with respect to the second closing element itself between a closing configuration and an opening configuration of said second transit channel; and characterized in that as a result of the insertion of said second male coupling within said second female coupling, said second closing element is able to contact said first closing element to displace it from the closing configuration to the opening configuration, and the end of the second male coupling itself is able to contact said first tubular element to displace it to said fastening configuration, said first tubular element being able to drag in its displacement said second tubular element to displace it to the relative opening configuration in order to place in communication said first and second transit channels (31, 29) together. - a base body associable with a trailer and wherein is defined at least a first female coupling, provided with a control line connectable to the braking system of the trailer, and at least a second female coupling, provided with at least an additional line which acts on the parking brake of the trailer and provided with at least a by-pass line communicating with an unloading tank; - at least a first and a second male couplings (12, 13) associable with a towing vehicle of the trailer and connectable to the relative braking system, where said first and second male couplings (12, 13) are connectable to valves able to send to the same, respectively, a working fluid at a first and at a second pressure and are insertable, respectively within said first and second female couplings (3, 6); where said second male coupling defines a first channel for the transit of a working fluid and has a first closing element of said first transit channel movable between an opening configuration and a closing configuration, - valve means able to put in communication and isolate between them said additional line with said by-pass line, respectively, as a result of the exit and the insertion of said male couplings (12, 13) from the relative female couplings (3, 6);