the switches go bad - either stick and send vacuum all the time or not send any at all. Check it out and let us know....

 

I just posted a thread asking for help with this exact switch! Did you ever figure it out? I'm still lost to what it is. If you follow the electric side, it goes around the back of the engine and plugs into the brake wires or ABS wires. Weird that there is no finding this anywhere!!?? Thanks.

 

Found it. GM part # 88880029. It is a kit.