The engine may be diesel, but the electric power distribution system for the cars is quite high-power. Wiki: "Head End Power" (HEP) power supplies the lighting, HVAC, dining car kitchen and battery charging loads. Individual car electrical loading ranges from
20 kW for a typical car to more than 150 kW for a Dome car with kitchen and dining area, such as Princess Tours Ultra Dome cars operating in Alaska. Because of train lengths and the high power requirements in North America,
HEP is supplied as three-phase AC at 480 V (standard in the US and Canada), 575 V, or 600 V. Transformers are fitted in each car for reduction to lower voltages.
480 V and 600 V power distribution is nothing to fool around with. There was no way to know if the HEP system was still producing power, if the car bodies were energized, or if live conductors were lying around.