Have been reading and looking at pictures. A post by Bremery kind of helped me. I have a 743 and installed a heater in the cab. Connected hoses from my re circulating heater which did not work. Now I seen some pictures on this forum page 2 titled 743. My question is going from the water pump to the heater and then back to the thermostat do you need a by pass of a valve or can you run direct? I assume in these pictures the object on the left is the thermostat? Sorry could not copy and paste to show pictures to better explain. I have them on an email if some one needs to see them.