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If you have a fuse that you've checked and it's fine I would check all the wiring and I mean all of it,you only need it to be split somewhere along the line and it'll cause you problems.
Might be wise to get an auto sparky to take a look at it as you may have fried the controllers if it was wired up wrong and you connected the leisure battery to it.Also when you say you bought it secondhand did you actualy see it working?
He must have a multimeter as he has 12.5v at the battery; or has benny got that from the Spring controller display? Now if he has got that from the Spring controller display then this means that he has power at the controller.