An operator presence system for a cotton harvester including an on-board cotton module builder, the system including a mount for installing a ground access ladder at a first position for providing access to a service platform for routine service and maintenance, and a second mount at a second location for installing the ground access ladder adjacent to a ladder segment extending to an upper region of the machine, the mount at the second location including a switch or other device for disabling or locking out at least a hydraulic system of the module builder when the ladder is mounted to the second mount, and which re-enables operation when the ladder is removed therefrom.