Did it have any lines running anywhere else? To the pump, for example? It could be a heat exchanger to help keep the coolant cooler during stationary pumping in hot weather, and to keep the pump from freezing in cold weather.
Hopefully one of the more knowledgeable fire truck guys will chime in here.
On your images, you should be able to attach 5 to each post. You have to select each image individually to attach it. And then hit "Done"
