If the wires are power, ground, front light, and serial, this would be my guess.
Power and ground are obvious, I'm assuming that is track power unless told otherwise. Front Light would be the front headlight output of the CC board. This would tell the Atlas board that the headlight is on and the ditch lights can be flashed. Finally the serial would be tapped off pin #24 of the R2LC socket, that's the serial output data that tells the Atlas board when the horn is active.
