Vacuum Lines

I just completed the rebuild of the suspension/brakes/steering/exhaust on a 73 Imperial. When I put the steering column back I found a vacuum line coming through the fire wall near the steering column. I seached around and it fit a fitting on the base of my steering column. (or so I think, as it was behind the column and I could not see it) I know a lot about these cars, but the vacuum system is something that do not know much about.

What was this for?
Author: Moseman