2018 Mazda 3 BN Fuse Box Diagram

On the last of the BN cars the engine compartment fuse block is where it has been since 2014 — left rear corner of the bay, next to the battery, behind a cover that pulls straight off. Mazda’s April 2017 handbook for this model year prints the same plate as every edition before it, so a 2018 block and a 2014 block are physically identical; only the assignment of a handful of positions differs.

Positions run in four rows across the block. Row one: mini blades 1 to 13. Row two: mini blades 14 to 26, directly beneath them. Row three: cartridge fuses 27 to 32 followed by mini blades 33, 34 and 35. Row four, offset one cell to the right: cartridge fuses 36 to 39, then mini blades 40 to 43 — with 43 carrying the instrument cluster fuse that the pre-facelift cars leave out. The module drawn above row one is the multiplex slow blow fuse, eight high-current elements in one sealed housing, and the unnumbered squares filling the left of the block are its relays.

For the final BN model year the left side fuse block stays in the driver’s-side footwell of a left-hand-drive car, at the bottom of the trim panel next to the door aperture, under a cover that lifts away without tools. Right-hand-drive markets get the mirror image of the same installation; Mazda’s name for the holder does not change.

The fifteen fuses are arranged as a long column of eleven and a short column of four. The eleven lie flat and are numbered 1 to 11 from the top; the four stand upright and are numbered 12 to 15, again from the top, and are shifted down half a step relative to their neighbours — which is exactly how Mazda draws them. Nothing in this block changed between 2015 and the end of production in 2018, so a 2018 layout also serves a 2015, 2016 or 2017 car.