its off my 98 4x4. it wasn't plugged into anything when i got it. is it something for the hubs to lock in 4x4?

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looks like the vacuum resivoir should have 2 vacuum hoses one to the intake and one to the firewall
it is part of the a/c basically, it's so your blower doens't blow to defrost everytime you go up a hill.... or if you had vacuum wipers they'd stop ask me how i know that one
hmm rolling hills and rain in a 67 cougar with vacuum headlight doors, wipers, and defrost on..... hmph