Image forming apparatus includes a photoconductive drum cartridge which has an opening through which toner is applied to an electrostatic image formed on the photoconductive drum. To provide more than one color, a development device includes four toning units which are indexible into alignment with the toning opening in the cartridge. Each toning unit includes an applicator assembly at the top of the unit which is movable with respect to the rest of the unit toward the toning opening. A resilient lift mechanism engages a pair of ledges at opposite ends of the applicator assembly and is actuatable to move the applicator assembly toward the toning opening. A sensor senses arrival of each toning unit in a position aligned with the toning opening. A logic and control in response to a signal from the sensor rotates a cam member which is resiliently coupled to the pins for moving the applicator assembly. The applicator assembly includes three positioning protrusions that seat on flat surfaces adjacent ends of the opening in the cartridge.