In which cab should the key switch be activated?

The key switch should be activated in the coupled cab end of the rescuing train because this is typically how control is established when two trains are coupled for assistance or rescue operations. Activating the key switch in the coupled cab ensures that the train crew can effectively take control of the rescuing train and manage its operations in coordination with the other train. This practice is essential for safety and communication during the process, allowing for a clear command structure when trains are coupled.

Activating the switch in any cab or the rear cab may not ensure proper control, as these locations could be far from where active intervention is needed, and could complicate communication or control between the two units. Using the front cab would also not be appropriate, as it may not provide the necessary proximity to oversee the coupling operation effectively. Therefore, activating in the coupled cab end is the most logical and effective approach.