I am not sure if this is true or not.....
but on my ARB I was having the same issues with one switch not lighting up unless the other was on... bla bla..
well the response I got was that it was actually the front switch that was not supposed to light up unless the rear was on, and I had to switch my wiring at the solenoid (I had them reversed).
I was told that it was "supposed" to be like a "safety" thing for the locker so that the operator was not just running on the front only locked while the rear was unlocked.
this could have just been a bunch of jibberish from the peeps to get me to leave them alone, but I switched the solenoids and I have not had any issues.
I still have to have the rear engaged before I can lock the front, but eh... I got a good deal on the units so I will just deal with it.
oh.. and mine are a bit older units as well, I have the older style switches. Not sure if that makes any difference.