When so equipped, the dynamo was often found mounted on top of the boiler just in front of the cab of the locomotive. It was controlled by a single valve inside the cab of the locomotive which allowed the engineer to supply it with steam when getting the locomotive ready for use or turn it off at the end of its use.
When operating, dynamos would run around 2400 RPM and generate 32 to 37 volts DC. They would have a 350 to 500 Watt capacity. Low wattage bulbs (15 watts?) would be used to provide light within the cab while higher wattage bulbs (100-250 watts?) would be used for headlights. Bulbs used in steam locomotives had to withstand the shocks and vibrations customary in this type of environment. Therefore, they often had heavy-duty filaments.