[W126 Coupe] Vacuum Lines

[L&D gardner]

Hi Folks
After my last post,where I was trying to get my passenger seat to lock(after
it was used to stop a falling person!!)I reconnect the lines under the seat
and tested with a Mityvac,and got the seat to lock at the seat location and 
also at the bulkhead @22hg,but another fault is preventing it from
locking, the dark red & yellow striped line on the bulkhead will not hold 
any vacuum at all,I have looked at the CD manual but cannot find any 
reference to the function of this line.Any advise gratefully received.

                                                                             
                                             Kind Regards Dan Gardner   1986 
560SEC Euro (220kw)