Piranha battery monitor - info needed.

Hi guys.
I have one of those Piranha battery monitors with the led read-outs on the front and am in the process of moving it to my other fourbie, the wife's x-trail. I previously had it wired in my Pajero just to monitor the battery level, but I intend to run a Engel fridge of the single battery and want to hook the battery monitor up so that it will cut power to the fridge if the battery drops below the pre-set level.
Does anyone know which wire does what and/or possibly have a schematic of the device. Mine has then push button so you can monitor two batteries, with blue/black/white/red wires coming from the back. I am not sure what model it is, but I got it about 5 years ago.
Any information is appreciated and can the cut-out voltage level be changed.

Thanks in advance.