If somebody has a picture of this it would help. I searched the FSM and the archives it wasn't their for a 85 12a. Or if somebody can describe I can try and draw a picture.

 

Once the coolant is hot enough to open the T-stat it goes out the top hose into the radiator, gets cooled and goes back into the engine. As for the heatr hoses it goes out the hose (or hoses if you still have the beehive oil cooler) on the driver side of the engine, through the beehive (if you have it) and the heater core and back down to the bottom of the engine via the hard line on the passenger side frame rail. Hope that helps....

 

Here is a little diagram based on what you said, plus what I'm trying to get at.
The previous owner cut off one of the hose that are going to the heater core and put a plug in it. I haven't seen where else is missing a coolant hose. Hence why I asked for flow diagram. This also doesn't have the stock intake manifold, was their something their before that would of feed coolant to the heater core?

 

Huh your picture doesn't look right to me (but it's been a while). The other outlet of the heater core goes to the coolant fitting next to the oil pressure sending unit on the rear iron.

 

On the 83-85 12A, where the beehive/heater hose connects to the block, there is a "T" fitting. If you don't have a "T" fitting under the beehive, you have an earlier model engine.

 

Under the beehive their is no tee, near the oil pressure sensor. Their is a tee after the beehive that goes into the rear iron. Like I showed in the picture. So what can I do?

I'm also trying to find a leak under the car. It's coming from the passenger side frame rail. Almost in the channel for the headers. I haven't seen any coolant inside the car. And if the supply line to the heater hose is missing. What is causing the leak? Coolant trying to backflow through the heater core?

 

The correct hose routing would be a tee fitting at the engine, with one hose going to the beehive, and the other to the open port on the heater core. The return port of the heater core also has a tee fitting, where the hose from the beehive hooks up, before returning to the lower hose at the radiator.

The coolant leak you are describing could indeed be coolant coming from the open heater core port. It could also be the heater core is bad.

If your engine does not have the tee fitting, get an aftermarket hose tee, and place inline at the engine, and route the hoses in the correct manner. Or, get a front mount oil cooler, and do away with the beehive.