Mine did this once. it turned out to be a 25p [car type] spade fuse which is inline from one of the batteries. It's effectivly a 'master' fuse and if/when it blows, EVERYTHING is off.
Scratch around in the console by the batteries and have a look.
it cost me 2 new heavy duty batteries, various fittings etc before they sorted it.
Ribcraft however where very helpful with the labour charges and also rewired it all on site for me.