Stepper motor housing pipe connection

In the process of changing the cam in my 500 and after removing the plenum I noted that there is a pipe connection on the stepper motor housing with no pipe connected to it. The connection is about the same size that would fit the vacuum advance pipe that runs from the dizzy to the plenum air intake. I can't find a pipe/tubing in the area that should run to this stepper motor housing connection, anyone know what its for and what it might connect to ?