Faulty 4wheel drive

Many possible causes check this out ,

First lay under the car and look on the back of the transfer box, there should be a nest of wires here - take a look for any damage wires and check the plastic connector from the 4wd switch is ok.

Tracing the vacuum hoses is a bit fiddly. The usual failure point is at the back of the hubs themselves.

Jack up each side and remove the front wheel. You should see two black semi-flexible pipes entering the hub. One of these pipes uses the vacuum to pull the hub on and one uses the vacuum to pull the hub off.

If they are not engaging then it is only the "on" pipe that is a problem - but I cannot remember which is which!.

Trace the pipe back check carefully for cracks and leaks. Do this on both sides.

If the pipes appear ok then it could be the solenoids which control the vacuum. These sit underneath the battery. First check if they are plastered in dirt. They have small filters on them to let the vacuum out (well let the air in - you know what I mean!) - these could be blocked with mud. Hold a finger on the solenoids and get someone to slip it in and out of 4WD - you should feel the solenoids operate. If not then the wiring is a problem. I would return to looking at the 4wd switch under the car at this point and check this out - you can short out the 4wd switch connector with a piece of wire to "force" it into 4wd