Vaccuum lines for heating and air conditioning

Model is a 1988 Mercedes 190E 2.3, girlfriend and I had to remove the complete dash on this recently purchased car to replace the heater core, we found a "Gray" colored vaccuum line laying on top of the wiring harness just behing the instrument panel not hooked to anything, I traced the line back through the firewall to a T-fitting on the intake manifold> We started to engine and let it run abit then shut it off noticing there was not vaccuum to lock the doors. Its obvious this line is a central player in the main vaccuum to operate the vaccuum operated doors, sun-roof, and the flapper valves on the heating and air conditioning ducts. My question is where can I get a copy of the routing of these vaccuum lines, we bought a repair manual but has no diagram of these lines and where they go. Please help. Thank You, Denny