I am assuming this is for the heater. It turns into a metal tube and runs along the back of the head to the bottem of the intake manifold.

Is this for the heater? Can I plug it temporarily to drive the truck, I'd just have no heat right?

 

it is the inlet heater hose to the heater core for the cab. you can plug it but make sure you plug bothe of them (the other hose to the left that runs into the firewall that your left hand ring finger is sitting on)