An assembly for mounting LED units or contact units for electrical systems for controlling industrial machines or plants, comprising: - a casing housing thereinside two or more fixed electrical contacts associated with respective wiring terminals for connection to an electrical circuit, said casing having at least one pair of lateral passages for accessing said terminals; - at least one LED circuit adapted to be inserted into said casing and having a diode for emitting a light beam and a printed circuit or PCB for the electrical connection with said electrical contacts; - at least one actuator adapted to be inserted into said casing and having a slider slidable in said casing with an upper end adapted to be associated with an external control and two or more movable electrical contacts adapted to be brought into contact with respective fixed electrical contacts upon the translation of said slider; wherein said casing comprises a housing for selectively receiving said at least one LED circuit or said at least one actuator, said housing being provided with an upper hole for connecting said diode with said PCB or for the exit of said upper end of said slider; characterized by comprising an anchoring cradle adapted to be removably arranged in said housing to allow insertion and blocking of said LED circuit in said casing in absence of said actuator, wherein said anchoring cradle comprises an axial plate adapted to be snugly fitted into said housing and having means for the removable fixing of said PCB and the support thereof into said housing and an annular projection adapted to be fitted into said upper hole and having at least one axial slot for the electrical connection of said diode with said PCB and/or for the passage of the light beam. - a casing housing thereinside two or more fixed electrical contacts associated with respective wiring terminals for connection to an electrical circuit, said casing having at least one pair of lateral passages for accessing said terminals; - at least one LED circuit adapted to be inserted into said casing and having a diode for emitting a light beam and a printed circuit or PCB for the electrical connection with said electrical contacts; - at least one actuator adapted to be inserted into said casing and having a slider slidable in said casing with an upper end adapted to be associated with an external control and two or more movable electrical contacts adapted to be brought into contact with respective fixed electrical contacts upon the translation of said slider; wherein said casing comprises a housing for selectively receiving said at least one LED circuit or said at least one actuator, said housing being provided with an upper hole for connecting said diode with said PCB or for the exit of said upper end of said slider; characterized by comprising an anchoring cradle adapted to be removably arranged in said housing to allow insertion and blocking of said LED circuit in said casing in absence of said actuator, wherein said anchoring cradle comprises an axial plate adapted to be snugly fitted into said housing and having means for the removable fixing of said PCB and the support thereof into said housing and an annular projection adapted to be fitted into said upper hole and having at least one axial slot for the electrical connection of said diode with said PCB and/or for the passage of the light beam.