Bob, you shouldn't have a vacuum switch on the dash. If you do, someone put it there. For that year J-10 that you have you should either have the Borg-Warner Quadratrac full-time four wheel drive, or the Dana 20 part-time four wheel drive. Only the late model FSJ's had the New Process transfer cases (NP229, NP231,...) that used the vacuum switch.
You probably have the Quadratrac, and that means that you are in four wheel drive all the time. You should probably check and make sure that your drivetrain is stock, or the guy you bought it from might not be being honest with you.
Check out http://www.ifsja.org/
i'm a member there. It follows the same format as here, but it is just for Full Size Jeeps. There are guys there with infinite knowledge about the big Jeeps, and there is never any flaming. The only dumb questions are the ones not asked.