1992 explorer automatic hubs.Button in dash does not engage $ whe

Check that the auto hubs for the front wheels are engaging and that the vacuum/electric actuators are working.

The power to the switch seems to be the issue. The vacumm switch is
just a normally closed switch,meaning only when it gets power, will it
send vacumm to the hubs to allow the 4wd to work automatically. You will have to trace the electric back from the switch,to see where it goes,
a relay or fuse. You may just have bad relay contacts. Good luck.
You can always run a toggle switch into the cab,to get the system
working until you figure out what's wrong in the mean time. Just a thought. Good luck.

Any time your dealing with a 4x4 system the best start is at you front axle. Its primarily a vacuum leak so check to see if the 2 vac lines are hooked up (its good to check the electric connections.). When your 4 wheel drive is engaged and the motors running you should have vacuum at one or both of thee lines depending on if your in 4 hi or low .
If no vacuum at axle check the Vacum switchs(the plug with 4 vac lines) on top of the transfer case it will have 2 feed lines(grey & green) they conect in to the into the vacum harness on back of motor (passanger side). A vacum schematic is normally located on the raditor core support (right under the hood next to hood release)
Hope this helps

With the vac line off ( if you are sure it was not the vent line ) the IWE ( Integrated Wheel End ) would have been locked on that side.
Operationally vacuum holds the IWE ( Integrated Wheel Ends ) out, and once vac is removed the spring engages the IWE.
Might not want to assume it is the IWE, best to check

Lift and support the front of the truck so the front wheels are off the ground ( take safety precautions, chock wheels, jack stands, etc )
Key on, engage 4x4 and try to turn the front drive shaft.
If it turns it is a problem with the transfer case.
If it doesn't it is a front axle engagement problem.

The 2004-2006 have a TSB for the IWE solenoid, where it can ingest water, and introduce it into the system. This is one thing to keep in mind.
This is a PDF copy of the TSB
http://my.voyager.net/~sscully/file_tsb06_08_15.pdf

You can check operation by installing a vacuum gauge on the vac line at the IWE. With the engine running, you should have vac on the line. When you switch into 4WD ( H or L ) the vacuum should bleed off, with a correctly functioning IWE solenoid.
This is a block diagram of the IWE vacuum operation


Quick test, if you pull the vac lines, and plug them, the IWE should lock in all the time ( pushing a dead axle ). If you switch into 4WD, it should work. If not, could be an issue with the transfer case ( best to test as posted above with jacking the truck up ).
Also is this an ESOF ( Electronic Shift On the Fly ) or MSOF ( Mechanical Shift On the Fly ) ?

I don,t think 2002 Explorers have manual locking hubs so solution 1 would be wrong

The front hubs are vac. actuated and the lines are know to get a leak in them. When it happens the front hubs won't lock.

Same problem here. Just replaced the vacuum actuator and it still does not work. Could not see any damage to the tubes either. However after I manually move the vacuum actuator I can get it to engage and disengage up to several times but it never lasts

Auto hubs locked up? Electrical relay faulty? May need servicing.
ToyotaED would be the EXPERT to ask on this one.

http://www.fixya.com/postBuddyProblem.aspx?budid=1150094

it can be done but it is a pain in the ***.....its like converting from an automatic to a stick......its a pian but could be done.

I miss spoke...What had happen was that my front end was turning but hubs were not engaging...finally figured out automatic hubs were bad... when my ex had it she had a bearing repacking done, but they also put grease in hub.. wore down parts.. hope that helps..