The vacuum line you marked in the picture goes to your air injection pump, which is a belt driven unit just above the alternator at the passenger/front of your engine. As the other post said, you are missing some other items from the picture as well. There should be a "Y" tube attached to the top of each switch looking unit (as I already mentioned, the one on the right is for your air injection pump vacuum line and the one on the left is for a vacuum line going to your egr valve). The "Y" tube coming out of the top of each unit connects both systems into a single vacuum line which should run the length of your rocker cover with the spark plug wires and then over to your intake manifold. Hope this helps. I also have a 1990 190e 2.6 I just rebuilt.