How does the diff lock work?

I've got a 300tdi engine and transmission on my trailer out of a Disco 1. All seems fine with engine and gear selection including hi and lo, but I can't get the diff lock to do anything. Whatever I do with the lever, if I turn one drive flange by hand, the other turns the other way.
The lever feels good moving left to' right, it's not ceased like the usual fault.

Is the diff lock simply brought in by the lever, or is there a need have engine power, even hydraulic pressure or electrical actuation?

Anybody got any ideas?

simple manual engagement ,try turning 13mm nut on spigot were linkage joins t/box clockwise ,it could be switch wound in too far or poorly adjusted/worn linkage

I'm pretty certain it's mechanical. Is the spigot turning on the top of the box? What happens if you turn the input shaft?

Is it me but int the flanges supposed to turn opposite ways.

yes if diffs not locked

Thanks for the replies guys.

The spigot on top of the transfer box is turning (but I don't know how much it needs to turn).
I have turned the input shaft with the engine, but haven't got it to lock. I don't know if it only comes in under load or something.
There's every chance the linkage is out of adjustment - I will look tomorrow.

its just a sliding collar that locks onto front output shaft dog teeth ,often teeth will need aligning by turning output a little or box itself

That's what I was hoping it was jamesmartin.

I'm going to try to turn the front flange whilst pulling the lever into lock position to make sure the teeth align while there is positive force on the collar.