4x4 Transfer case parts etc. 1994 Blazer

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OK once again another question about a 4x4 transfer case. On my buddys 94 blazer the 4x4 wont do anything, wont engage at all. It is a pushbutton system similar to what our crews have, of course different buttons. Sometimes when you push the button you can hear it making noise when stopped but no lights indicate anything.

When I was checking things out back in april I found the diff cable to be frozen, so ordered a new one and will install that. The driveshaft was removed by the previous owner because of the diff cable being locked it was "stuck" in 4x4 I was told. I am assuming that one of the two things on the transfer case might be dead also. I havent been under the truck since April and I am trying to figure out do I need the electrical switch or the vacuum one? They have both parts on ebay and I want to make sure I get the right thing. Do these trucks use both types? I can get each one for about $20 a piece and I was thinking of just changing them both to be on the safe side. Any thoughts?