Toyota Hilux differential locker

I have a Toyota Hilux and I have had problems with the differential
locker
Sometimes the light comes on and no split
Sometimes I have the light on contantly and split even using it
normally with two wheel drive
It is difficult to know what to do to let it stop being split
I have tried to use 4wd low and set it on and off but it just stays on
I have taken the car in to Toyota to get this fixed several times last
few years

Even got a new motor last year

Any suggestions on what to do?

Is this a know problem?