The vacuum port on the top of the intake manifold splits and sends a vacuum line to the right and left side. The vacuum line running to the left side (drivers side) doesn't hold vacuum. This line branches off to two vacuum lines running in to the back of the dashboard. I disconnected and plugged that branch. Would like to know what these two lines do?

I was thinking these lines would be contributing to the low vacuum measured earlier at 7" at this very same port. But these losses would compound the already low vacuum because when I tested I removed these lines and connected the vacuum gauge.