I am fimiliar with the two contact-single swicth used on the later Turbo V6's. I am not sure exactly how the three contacts-dual swicthes work (third contact is ground?)
Try removing the connector for the bad swicth and ground it to something. If the yellow/orange light comes on then it is a simple, normally open pressure swicth.
They have been long discontinued by GM, but there should be many subsitutes around. Nitrous Oxide Systems use these types of switches. They are also know as Hobbs swtiches. Find one that operates at the PRESSURE you want. An adjustable unit would be better.