The additional red pipe probably supplies compressed air to the locomotive.

The next picture showing the coupling also reveals that their are three compressed air pipes between the coach and the engine.Two are the regular Green Brake pipe and White Feed pipe and an additional red pipe which is probably the air supply pipe to the locomotive.The yellow pipe in this picture appears too flimsy(and its not even clamped on the engine side) to handle compressed air at 8 to 10 kg/cm.I think this yellow pipe may be a water pipe to supply additional water to the loco from a tank in the coach.