I converted this Bachmann Large Scale Heisler locomotive from track power to battery power and Blunami BLU-4408 decoder. I tied into the existing Bachmann circuit board and was able to keep the cab light, the flicker box light and the front and rear headlights as well. Fun project and actually much easier than I anticipated. Enjoy!
Sometimes all it takes is the willingness to give things a try. Glad to see you making things happen!