Abstract: A control unit, for example, a light dimming unit for controlling the intensity of brightness of a lamp load connected in series with the unit, includes a switching potentiometer for serially connecting the unit between a supply line and the load and for selectively adjusting the current delivered to the load. The switching potentiometer in the unit includes a shaft mounted for both rectilinear and rotary movement. The shaft is normally urged by a spring in a first axial direction, to urge a wiper mounted on the shaft resiliently into electrical contact with a resistive strip. A ratchet means carried on one end of the shaft actuates a snap-action switch which includes an armature, movable between first and second stable positions by the ratchet means when the shaft is moved in a second opposite axial direction to disengage the wiper from the resistive strip.