Heater hose routing?

[myascape]

I have a very nice 1981 1/2 ton pickup that's a real survivor. I'm the second owner, and she has just over 79,000 miles on the clock. My 250 runs like a top now that I've restored all the vacuum lines to stock and found a rebuilt carb.

Now the question: What is the heater hose routing? I know it seems straightforward, but there's a "mystery hose" on the driver's side of the block close to the bellhousing. It's currently running behind the engine, over the bellhousing, and sitting capped off on the passenger side framerail.

Does this "T" into the hoses running to the heater core somewhere? If so, which hose? I'm assuming it's there to keep temperatures stable around the back cylinders to help keep them from warping. I'd like to figure it out before I go adding a tank heater so I can get it right. Does anyone have a picture?

Thanks in advance for your knowledge!

 

[vwnate1]

Mystery Hose

I don't know this one....

Maybe a $29.95 FSM would help ? I glean much from looking closely at all the pictures .

 

[myascape]

I've got the manuals except for Motor's from that era. Just about every example I've seen so far deals with a V-8; the Inlines tend to get left out.

I'm considering just teeing into the mystery hose at the heater core and tying in the electric heater in there somewhere.