Cary, that is a central distribution block for the coolant.The lines (2) come from the engine,1 is a supply line , the other is a return line. The other 6 lines coming out of the unit will go to the cab heater, bunk heater and the other 2 would likely be there to connect to an auxiliary power source (generator or APU) or it may just be there for future use.Same thing as the supply lines,1 is a supply line and the other is return coolant.