I wanted the Mazda Bongo’s electric curtains, interior lights, and similar accessories to run from the leisure battery instead of the starter battery. Rather than rewiring everything, I made a simple but effective modification at the fuse box.
Important: When doing any internal wiring in your vehicle, always include a fuse as close as possible to the battery output. This helps protect against cable damage or short circuits if the wire gets pinched or worn.
I installed a 20A fuse at the leisure battery output and ran a cable from there to the fuse box. At the fuse box, I soldered the ends of two cut fuse taps (fuse connector blades) to this cable and inserted them into the bottom legs of the relevant fuse slots. That way, the electric curtains, interior lights, and the cigarette lighter socket are now powered by the leisure battery instead of the main one.
Update: The car stereo was also powered through the cigarette lighter socket. However, I discovered that the aftermarket audio system I installed draws too much current, even when idle. So I reverted the cigarette socket to the starter battery by reinserting the original fuse.
Above: 2002 Mazda Bongo 2.0L standard fuse box layout for reference.