Replacing the heater core and found this sensor strapped to it. It is shown in the Factory Workshop Service Manual (page 50 - 7/8 ) called a sensor line, but have no idea what it does or where it connects. The new one I bought from Vicks didn't come with one.

the original heater control valve used that to help regulate temperature, it would actually close the heater valve to keep the heat from getting too hot. lol but the replacement valves do not use it, throw it away as if it is not part of the original valve it is broken anyway

Thanks Beek. Wasn't planning on using it. Just didn't understand why it was there.