A gaming machine for conducting a wagering game includes a cabinet having a top box mounted on a main body. The top box has a door for allowing user access to an inner area of the top box. A lock assembly in the top box locks/unlocks the door and a release assembly in the main body operates the lock assembly. The lock assembly and the release assembly are configured to automatically engage one another when the top box is mounted on the main body. Thus, no manual connection is needed between the two assemblies and the lock assembly may be preinstalled independently of the release assembly. Moreover, any suitable top box design may be used with the lock assembly, and any suitable main body design may be used with the release assembly. This allows the top box to be selected much later in an assembly process than previously possible.