What must occur on a trailing motor when the auto coupler control MCB trips?

When the auto coupler control motor circuit breaker (MCB) trips on a trailing motor, it is essential for safety mechanisms to activate. The illumination of the emergency brake light serves as a critical safety feature. This action provides a clear visual indication to the train operator and passengers that there has been an issue that requires immediate attention and could potentially affect the operation of the train.

The emergency brake light alerts everyone on board to the situation, indicating that the train may need to stop or that there is a need for increased caution. This response is vital in ensuring safety and maintaining communication with passengers about the train's status during a fault condition.

In contrast, other options such as making no changes or having operational lights turn off do not provide necessary safety responses in the event of a trip, and activating passenger information systems when the coupler control MCB trips is not a standard procedure in this context. Thus, illuminating the emergency brake light is the appropriate and correct response.