When operating from another car than the leading one, what is the maximum position the controller can be advanced to?

When operating from a car other than the leading one, the maximum position the controller can be advanced to is "Series." In a train setup, specifically with electric multiple units or similar configurations, series operation allows for controlled acceleration while ensuring that the train can manage its power delivery efficiently across multiple cars.

Advancing the controller to the series position ensures that the train operates within a safe power range, which is particularly important when not using the leading car. It helps distribute the available power effectively throughout the train, reducing the risk of power overload while allowing for adequate control over operations.

Other positions such as full throttle or neutral are not appropriate in this context. Full throttle could lead to a loss of controllability or overload conditions, while neutral would halt any power to the wheels, leading to no movement. Slow mode could imply a restricted speed but may not represent the maximum power allowable under these operational parameters. Therefore, series is the optimal choice for maximum effectiveness when controlling a train from a non-leading car.