Why wouldn't 4-wheel drive be engaging on a 94 S-10 Blazer when the fuses are good?

Check the vacum axuator(sorry bout the spelling) a vacum line pulls a cable in 2 engage the 4by sometime a dirty switch will not allow all the power to pull in the cable to engage the drive,the vacum looks kinda like a old cruise control pump,might b under your battery box or by the radiator

On the '94 S10 Blazer the vacuum diaphragm is located under the battery tray. You must remove the battery as well as the tray to access it. This diaphragm pulls a cable which is connected to the front differential and engages the front axle when you put it in 4wd. It is possible that the vacuum line is broken, disconnected or leaking. It is also possible that the diaphragm is leaking or the cable is broken.