Hi Benji.
I don't know about the rear control box but I have heard of the rear isolator switch jamming or not connecting. It is worth removing the switch panel and cleaning the units, if you can find your way around a wiring diagram you could bypass the isolate switch, or try a spare that you know to work from a donor vehicle.
I'm refering to the 300 series here, not sure what you have but hope this helps.
Good luck.