It is recommended that a physics cable be its own component, so create a new component and add a physics cable behavior to it, and then save the component.
From there, add more pins as needed to make the cable stable and bendable at certain points in its length. That is, create a new node for every additional pin needed. How? Use the two pin nodes as a reference and follow the naming convention, e.g. Pin_3. Those two pin nodes are added automatically for you when you add the Physics Cable behavior. Each pin requires a physics entity behavior and needs to have the right name.
Refer to the Behaviors Reference and Tasks > Physics sections of help as needed about the properties. You can also refer to the Nvidia Physx link provided in the Help as well as the Unity reference guide since both software use Physx. How the properties are implemented may differ, for example different default values.
However, customizing the cable is the hardest part and requires testing on your own. First, move the first and last pins of the cable to the needed anchor points. That is, go to Modeling tab, and with a pin node selected, use the Move tool to drag the pin to the desired location. Next, set its Anchor property. You could also try using the Attach command to set that property. But note that attaching won’t move the pin! After the anchor points are set for the beginning and last pins of the cable, run the simulation and see how the cable moves in its default state when affected by gravity. I believe the end points hang and swing by default, but I don’t remember. Anyway, the cable has properties for defining how the end points should move, e.g. swing like a drawbridge, fixed like a connected/coupled joint, or have some movement like a tensioned chain side rail of a bridge.
Reset the simualtion as needed to return to the initial state of the cable. From there, adjust the stiffness of the cable itself and run the simulation and move the robot through a simple program to see how the cable moves. If you see some bubbling or breaks in the cable, it is either too stiff or not long enough. Note that a cable consists of capsules, small oval shaped geometry generated along the length of the cable. If the Length property of the cable is zero, the length is automatically calculated based on the end points, etc of the cable. In some cases, you can try giving a fixed length. But to avoid breaks, consider testing the tension and velo/pos iteration properties to get the needed result.
It is a challenge, my friend, so for cables consider using geometry instead of the physics cable for robot dress packages. For example, use one of the KUKA robots in the eCat as a template for creating your own cable from geometry.