headlight vacuum switch

[bloodknock]

Hello Folks
another job underway alongside sorting dashboard is the vacuum circuit. My car came off the road in th mid seventies, with very low mileage / usage. I believe that most of the components are servicable, however, before installation I like t check them out.
The vacuum headlight switch looks fine and mechaniclly feels reasonably smooth, but i want to test functionality.
Can anyone tell me which feed is which, and how the valve should behave when functioned? Is it just open or closed, or does it vent as well?
thanks
Bob

[ericbushby]

Bob, yes it vents as well. It is a three port (change over) valve and you can test it by blowing through it, or sucking if you dare!
The missing third port is not obvious because it vents to the inside of the valve assembly.
Eric in Burnley

[billwill]

The middle port goes to the lamp lifters and the first port goes to the engine sucking and as he says the third port has no pipe, but allows ordinary air back into the lamp lifters.

There's a detailed repair report on this site somewhere with pictures.