If this is a prewar motor, there is no controlling the bell by a transformer activated button. The bell is only be controlled by the activation lever on the motor itself, as the bell ringing mechanism is a mechanical mechanism that is operated by a gear.
It is my understanding that the motors can be modified to have the bells move; however, I am not sure how to do it. I believe it entails adding a brass rod to connect the physical bell on the top of the engine to the mechanical bell ringing mechanism inside of the boiler.
