Route the Z-stepper wires as shown in the picture.

Use a zip tie to constrain it to the mill_stepper_cable_managment printed part, then through the mill_z_tower_top printed part and inside the Z tower. Finally exit at the rear, above the Y stepper and into the electronics enclosure or your desired location. Leave an extra 300mm (at least) to route it to the controller and crimp the connector.

Cut the cables to the final length, double check if the cable has the appropriate length to reach the final position of your electronics enclosure before cutting.

Label the cable at the end, with a piece of duct tape for example.