It wasn't mine, and I just happened to be at the right place at the right time. The owner mentioned it was an older model. This one had a bundle of cables running from the cab to the tender, and he said the newer ones had the cables enclosed in an L-bracket that plugs up into basically the bottom of the cab for improved realism. Beyond that, can't help you. I know a little about HO, but not O-gauge.
Apparently that is the original MTH Premier Berkshire: 20-3032-1, made in 1999.
MTH adapted QSIndustries (QSI) circuit board reverse units and sound systems. They were called Proto-Sound. A thick black round cord connected circuit boards and a rechargeable battery in the tender to the motor, lights and smoke unit in the locomotive. A black T-shaped plug was pushed into place under the cab.
The L-shaped bracket is probably a wireless drawbar, a new innovation that eliminates the thick black cord and plug.
After MTH introduced Proto-2 command systems, that original system was called Proto-1. Like QSI products, it was designed for Lionel postwar transformers and the full sine wave they produced. Some newer transformers produce a "chopped" sine wave, and (with the occasional exception) they don't work well with Proto-1.
Although Proto-1 is a common term now, it was coined after Proto-Sound systems were superseded by PS-2 and PS-3. Boxes, instructions sheets and parts lists were printed Proto-Sound by QSI.
Proto-1 is designed for conventional operation: transformers control trains by varying or cutting off track voltage.
Proto-1 electronics have to be replaced by PS-2 or PS-3 (no battery) upgrade kits to use command control - 16 to 18 volts in the track and a hand-held remote that transmits radio signals to locomotives.
Some operators buy Proto-Sound locomotives at reduced prices and upgrade their electronics.