datsun210cali

I have a 1981 Datsun 210 L4 1.5L A15 manual that I am currently trying to get repaired so it will pass smog here in California. I have been told that it needs a "Manifold vacuum switch" but I cannot locate one. It is a round electrical plug that comes out of the wiring harness on the front lefthand side by the carb. it is round about an inch in diameter and has 3 female holes. If anyone has any information about where I could buy one or if the part I need is in fact called that, I would greatly appreciate it. I have pictures the smog shop sent me of the plug that the switch apparently goes to that i could send to anyone who is willing to help. They have had it a month and for some reason cannot seem to get this part. Thanks!!!