Here is the HVAC vacuum diagram for your truck:
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You are probably asking where to connect the vacuum source hose (item 45 in the image), correct?
I don't know much about TBI intake systems, so I can't tell you where to get full manifold vacuum on the throttle body. Somebody else will know.
But, in the mean time, look on the intake manifold (center - near the back). There should be a tapped hole.
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It may be plugged or it may have an adapter screwed into it. There may already be vacuum tubing connected to the adapter - if there is one.
You can use that port/adapter to supply your HVAC control system with full vacuum.
Run a hose up to the firewall, tee it off to the left and right. The LH side runs over to the vacuum reservoir (outboard of the master cylinder) and the RH side connects to the HVAC system inside the cab.
