Hiace Electrics between camper batteries

Hi, I only hope you can give me a clue!
Toyota Hiace camper van 2.8 diesel 1991 in the UK with dodgy electrics
I noticed the other day that all the electrics to the leisure battery were not working. When I switched on a switch to turn on the fridge, lights inside the back, fan on the roof etc, nothing worked! Having done a few tests, I turned the ignition switch half on (as you do to switch the radio on for instance) and the lights came on. Everything works. So I left the fridge on with the key in the ignition so it was on and by morning, the main battery was dead. It seems that nothing is working from the leisure battery and power is coming straight from the main battery. It does seem to charge though when the engine is on.
Has anyone any clues cos I don't. I'm no genius when it comes to this sort of thing. Can take a laptop to bits but when it comes to this sort of thing, I haven't a clue! The battery is loaded and fine. I have tested it and it's good. It's just that nothing seems to work from it for some reason. Would there be a fuse somewhere, or is it something to do with the bit you put the key in? Only guessing really..

Help

Sounds like the split charge relay has gone maybe....can't tell you where to look....I'd just trace the positive wiring from the leisure battery backwards until you find the problem

chrisandhiace wrote:

Sounds like the split charge relay has gone maybe....can't tell you where to look....I'd just trace the positive wiring from the leisure battery backwards until you find the problem

Thanks for your idea. It was actually a 15amp fuse down by the leisure battery which had blown. I reckon your answer was very credible under the circumstances though