Hi all, please take a look at my YouTube video that I have made describing the issue I am having at the moment.
https://youtu.be/RXYwtEqBcsQ

Thank you so much.

Sometimes you have to move slightly forward to get the light to come on, which is normal.The light on mine won't come on at all, caused by a worn linkage. You have to remove the centre console , gear knobs and gaiters, drill out rivets to get to the linkage. I bought the new parts for £30 but have not got round to fixing it yet. You can also run wires from the battery to check the light is working, you can get to the connector from underneath. You need the light to check that there is no transmission wind up before you get back on the tarmac. You can Jack up a wheel to release wind up if needed.

Thanks @white_disco
Sorry about me being a newbie - but what is releasing the wind up?
Cheers.

We were all Newbs once! Wind up is just where the transmission gets under tension if it's driven on dry / hard ground with the diff lock on. Probably no need to worry at the moment. Try driving forward or backward in diff lock to get the light to come on. If not, run some wires to the diff lock wiring connector on top of the transfer box to check the light works. If it does, start investigating the linkage. If you'll never go off road, no need to bother fixing it.

It could be also a blown bulb. Had that happen many times to Dad's truck. My Disco has the opposite problem, sometimes the light wouldn't go off. I then found out that you have to get it up to speed to disengage the light. I'm thinking yours could be as simple as a blown bulb but could also be something like a worn linkage like mentioned above. Some people also have problems with their light staying on and take the bulb completely out (so they can pass WOFs, NZ equivalent to a MOT) so seeing as you've just bought it, that could be something too to check. What I can say is your transfer case and difflock looks to engage/disengage and move from hi/lo nicely

Yes good call, could be the bulb itself.

Thank you all, I have since jacked up one front wheel whilst the diff lock is engaged but the wheel still spins freely, does this mean it's not actually engaging ? Looks like it must be a worn linkage perhaps? Any help much appreciated.

No, as the central diff lock has no bearing on the operation of the axle diff.

discool said:

No, as the central diff lock has no bearing on the operation of the axle diff.

Click to expand...

In English for the op please

So does this mean the diff lock could actually be engaging ok ?

There you go, I did the search of the Forum 4U. Simples

Testing your differential lock to see if it is engaging and disengaging.

If you aren't sure if your diff lock is engaging or not, here is a quick way to test it. First the indicator light on the dash is not 100% accurate in determining if the diff lock is on. A bent linkage can make the light stay on or stay off regardless of what the diff is actually doing. Second driving on the highway with the diff lock engaged will cause odd handling, especially around corners, chirping of the tires, and ultimately destroy your transfer case or shatter your drive shafts. So it is important to know if your transfer case lever is properly engaging and disengaging the diff lock.
Start by attempting to engage the diff lock with the lever. Then jack up one front wheel, just one though. Throw the truck in neutral with something blocking the rear wheel so it doesn't roll off the jack. Try and spin the wheel that is up in the air. It should not spin if the diff lock is engaged.
Have someone sit in the Disco and move the lever while you try and spin the tire.
If the wheel spins when the diff lock is disengaged and doesn't spin when it is engaged then the diff lock works. Test it both ways. You may want to try this with the back too, but if one works the other should.
If you understand how the diff lock works you can see how this tests it. With one wheel on the ground the only way a free will can spin is if the lock is not engaged since on a Disco the lock is basically hooking the axles together for lack of a description. Something to understand is that while the Disco is all wheel drive, unless you have aftermarket lockers on the axels you don't have "4 wheel drive". Without the difflock engaged all the power will go out one wheel if it loses traction. With the diff lock engaged the transfer case is splitting power evenly between the front and rear so you can still get stuck if you lose traction on a front and a rear wheel at the same time.