I'm trying to sort out some burnt / mis-routed vaccum lines on my 03 ZR2. Why does the tranfer case vaccum switch have a 3 line connector. I would think that 1 goes to energize the front axle actuator under the battery - and 1 goes to vaccum source (T off EGR valve on my truck). Where does the 3rd line go?

Also, does someone have a link to a good vaccum diagram for this circuit. I have a Haynes manual and Alldata subscription but neither is much help.