What is the first step for removing a wall (auxiliary) trolley from a car?

The first step for removing a wall (auxiliary) trolley from a car involves ensuring that power is safely disconnected to prevent any accidental activation or electric shock during the process. Shutting off the switch box effectively interrupts the electrical connection, allowing the engineer to perform the removal task safely.

This step is crucial for safety protocols in train operations, as working with electrical equipment without de-energizing it can lead to hazardous situations. The other options may be relevant during the overall process, but they either follow this safety measure or pertain to specific functions that do not prioritize the immediate safety of the work being conducted. Therefore, ensuring the switch box is shut off is the logical and safe first step in the procedure.