What year windstar?
Are you talking about the box that is hidden behind the accumulator canister in this picture?
http://rides.webshots.com/photo/2077...11220610tpjsMq
You might go to a dealership.....as they have the best parts breakdown that I have seen......with part numbers, etc.
I tried looking on Rockauto and Y2KFORD.......and did not find a parts breakdown that gets to that vaccum line.
You could try calling Y2KFORD ( they also have the ability to ask questions on their website, in addition to phone number to talk in person) and asking them......and they might give you a good discount price through their internet site.....as they do give good prices and seem to be very helpful.