1987 300 tdt vacuum line question

[fly fishing]

First time posting, I hope this question belongs in diesel discussion.
I just replaced the vacuum pods under the dash. Upon reinstalling the dash I found a large diameter Black vacuum hose (by the speedometer cable and steering wheel post) that I did not recall unhooking. Therefore I also do not know where to attach it. I believe it starts at the vacuum filter under the air cleaner in the engine compartment. It then travels through the engine compartment and through the firewall near the brake master cylinder.
What is this vacuum lines function ?
Thanks much, Ken

[Bio300TDTdriver]

Do you mean the line that goes to the brake booster? I don't believe there is a large vacuum line that goes through the fire wall. At least I haven't seen it on my car. I did the vacuum pods as well.

[Jeremy5848]

It is a vent line. Leave it alone, it is where it is supposed to be and connected to nothing. The vacuum system sucks air in through that line when vacuum is "released." The idea is that the air under the dash is cleaner than the air in the engine compartment.

[fly fishing]

I am greatly relieved to know I'm not destined to take apart the dash chasing a connection to who knows what, where.
Thank you for your reply and Information
Ken