What's with the AC hookup on the Buckingham Branch #8? I never saw that before.
I suspect it's a crankcase oil heater, possibly a battery charger. Despite what the sound cards might imply

, cold locomotives are difficult to start. It used to be common practice to leave parked power running overnight to keep the oil temp up for assurance they would be running for the next day's work. Pollution rules, fuel costs, and noise abatement laws made that practice undesirable, so a partially warm oil bath eases the start sequence.
Notice that there are four of these outlet posts, so all of their power must get this retrofit.