Euro Light Switch Question

I am in the process of enabling the light adjuster for the euro lights on my 1980 300SD. I have all of the necessary parts and can make the system work, I just have a couple of questions. 1) when I connect the vacuum tubing in such a way as the switch operates the lights, only one nipple of the switch is used. Can anyone shed some light (pardon the pun) on how the switch is to be plumbed? 2) when the tubing is all connected, and the system works great. (IMHO) I can hear a hissing sound from the switch. Is this normal, or do I have a bad switch? 3) I assume that the system needs full vacuum for the highest light position, then bleed-off down to no vacuum for the lowest. Is this assumption correct?
Thanks for your help.
Robert

[wolfgang]

Use the search function

[speedy300Dturbo]

Here is the official vacuum circuit wiring.

Nice diagram!

Thanks for the diagram! It looks as if it is for a gasser, but I can tee-off the vaccum from the ACC line running into the firewall.