OK, a bit on how 4x4 works: (With thanks to club member, Doug).
Locking the centre diff is not the same as locking all 4 wheels. the centre diff sits in the transfer case and provides for differing speeds between the front and back axles. the axles turn at different speeds around a corner because only the front wheels are articulated and thus travel a different distance. there is still a differential on both axles to allow for speed differences from side to side of the vehicle. with an open centre diff you can drive on road in 4x4 mode. all 4 wheels are
receiving power. unfortunately with all 3 diffs open like this it only takes loss of traction on one wheel to stop the car from being able to move forward. this is because the centre diff sends power to the fastest axle and the axle diff sends power to the fastest wheel. pretty much all land rovers are setup like this for driving ON ROAD. this is what you call "full time" 4x4.
With a centre diff locked the two axles are forced to turn at the same speed. there is still a diff on either axle to account for side to side wheel speed differences. it now takes a loss of traction on 2 wheels to stop us moving forward. one at the front and one at the back. because cars are designed with only one set of turning wheels (at the front) the path
traveled around a corner is different for the front and the back set of wheels and the axles turn at different speeds. with a locked centre diff they are not able to turn at different speeds unless one set of wheels (the front) is able to briefly lose traction. this is usually
refered to as "scrubbing it off on the tyres". obviously this can only happen on loose surfaces. if you try to drive in this mode on road you risk something called "windup". because tyres have high grip on
tarmac surfaces it is more likely that the speed difference between the front and back axles around a corner are not going to result in loss of traction. this can result in
enormous stress on your transmission and can damage or even break it. only use a locked centre diff on loose surfaces!
A rear diff lock locks the rear axle diff so that the wheels on that axle cant move at different speeds to each other. this is great on loose surfaces where the inner wheel in a turn can scrub off the extra speed but can be extremely dangerous on road as your steering ability becomes very limited. with the centre diff locked AND the rear diff locked it takes a loss of traction on 3 wheels to stop us moving. 1 at the front and both of them at the back.
Early (MK1) Pajeros and Delicas don't have a centre diff at all. these are classic "part time" 4 wheel drive machines. when they are put in 4x4 mode the front and rear axle are locked together.
The transmission selection lever next to the gear stick has 3 modes: 2 wheel drive, 4 wheel drive high ratio and 4 wheel drive low ratio.
Most (but not all) of these have auto-freewheeling hubs on the front wheels. what these do is disengage the front wheels from the front axle when in 2 wheel drive mode and engage then when in 4x4 mode. this is good because there is no point for the wheels to be driving the front
drive train around when in 2 wheel drive mode. thus it saves wear and tear and reduces friction and thus fuel
The MK2 (1991 on) Pajero has something called "superselect". this gives you the ability to use 2 wheel drive or 4 wheel drive with locked or unlocked centre diff at will. some also have the option to lock or unlock the rear diff.
As far as i know there has never been a factory model with a front diff lock. some mad people have managed to put aftermarket lockers in the front diff. this is very difficult to drive in anything other than a straight line and can break your power steering too.
The only factory fitted locking rear diff is manually operated, ie you will have a switch for it on the centre console. Most not fitted with the locker will have a limited slip differential, (lsd), which operates at all times on hard or soft surfaces but does not supply anywhere as much traction as a locker.
Basically an lsd has a mini clutch pack inside it and uses friction to provide a proportion of the power to the wheel with traction. these diffs have a sticker on them warning you to use lsd diff fluid instead of normal gear oil. if the sticker isn't there anymore
because its been scraped off on a trail etc then the only sure way to find out for sure is to jack up one side of the car and try and drive off the jacks. not that i recommend that at all.
If you want to learn about 4x4 technologies take a look at these links: