Chevrolet Repair: 4-wheel drive on s-10 pick-up, swithches, electric vacuum

Question
The 4 wheel drive on my 1994 S-10 pick-up will not engage when 4 wheel is selected. I know that there are vacuum swithches in the system. Which swithch is most likely the culprit.

Answer
Hello Charles,
If you have the vacuum actuator on the front axle, it may be stuck, or the cable broken.
The actuator diaphragm is on the right front fender area, possibly under the battery.
I believe there is also an electric vacuum control valve, so a fuse is possible also.

Van