My 1994 Chevy S10 will not engage into 4 wheel drive.

Start with tthe fuse. If thats ok then check the valve under the battery tray(one or two of the bolts comes up from the wheelwell). It looks like an old cruise control module. The rubber tends to get old and brittle. It won't hold a vacuum to engage the transfer case. Look at the vacuum lines as well make sure they're not sucking air as well. If both the valve and lines are ok it could be the switch on the dash, the actuators at the front axle, a broken wire or a bad transfer case.

I've had a handful of these over the years. I'll bet the electronic 4wd switch on the transfer case is bad. Its a common problem on those vehicles. LMC Truck actually makes a old school choke style pull cable E-switch delete kit that solves this issue permanently. just pull to engage 4wd, and push to disengage. Obviously you can just replace the switch for about 40 bucks and chances are you'll be good to go for another 4-5 years.

my S -10 chevrolet 4wheel drive not working ,fuse good ,replaced with new switch on transfer case , all lights work on dash , but the one light flashes on and off , what could be wrong .