That is a SWMT. Switching Motor Transfer, I think is what it means. It's more or less a slug. It recieved its power from the mother unit, in this case, Chessie used their GP39s.
Mark, though i don't post every time i download your vids,(sorryops i DO find them VERY ENJOYABLE, and WELL DONE!:thumb: cant wait to see your next one:thumb:. THANKS for posting them:thumb:. -Deano