I thought the Mity-Vac test would at least work on 0, but there may be a continous bleed from the switch that prevents the Mity-Vac from pulling enough vacuum to move the actuators. It makes sense if the switch bleeds off 5-6 in Hg even in 0 (from 17 to 11-12).

With the switch installed normally, try capping/plugging the green A/C line, then test the lights. If that doesn't work, also cap the central locks. This basically diverts all vacuum to the switch. If it doesn't work in this set up, then you may have a faulty switch.

Or - and I know it sounds silly - change the settings on your ACC. If you substitute "seat backs" for "light actuators" the same thing happens my car. I can't draw enough vacuum to move the locks, even though all components test okay in isolation. When I change the ACC setting, they move.

You might be able to "borrow" the A/C vacuum reservoir. Do you have a check valve with red/gray and green/yellow lines exiting it? The red/gray is supposed to go to your A/C reservoir inside the left front fender (behind the wheel liner). Do you have a T-connector you can install there? Hooking your lights there would add a continuous bleed to the A/C system, though.

Check here for more info: http://images.google.com/imgres?imgurl=http://i25.photobucket.com/albums/c70/cyberbach/VacuumValveSteeringLock.jpg&imgrefurl=http://www.benzworld.org/forums/w123-e-ce-d-cd-td/1456119-another-vacuum-problem-need-help-2.html&usg=__gOpju3wL66nSv1ViHsVsX6y2tas=&h=307&w=365&sz=14&hl=en&start=11&um=1&tbnid=79QetIg8ub3B4M:&tbnh=102&tbnw=121&prev=/images%3Fq%3Dmercedes%2Beuro%2Bheadlight%2Bvacuum%26hl%3Den%26rls%3Dcom.microsoft:en-us%26um%3D1


and here: http://home.comcast.net/~phantoms/vacuum/heating_ac.jpg

http://home.comcast.net/~phantoms/vacuum/heating_ac.jpg