Vaccum hose for door locks: Where is it

[Helge Wunderlich]

I am planning to install a remote control for the door locks in my
1984 Audi 100.

Normally, the driver's door is not vacuum operated at all, so I have
to make some modifications. The bellow is modified and ready to be
vacuum powered, so all I need is to tap into the hose somewhere, and
connect to the bellow in the driver's door.

Where do I start searching for a suitable place to tap into the vacuum
hose so I can route it into the driver's door ?