When you plug the 4 pin black connector back in that board it will be connected to track power. If you have a AC transformer see if it runs at all and if it reverses. That board is unique to a few K-Line engines. Not many have documentation on how it works and I know I have not tried running mine without it being connected to a radio board, aka R2LC in Lionel speak. Try it, as you have nothing to loose.
Pete