Fuse box component

While removing each fuse in my 2004 Espace 3.0DCi to try and trace a battery drain I accidently dropped one of the fuses from the engine bay fuse box, problem is I realised it wasn't a fuse as its slightly bigger than a fuse and goes in the location as pictured below.

I cant find an engine fusebox diagram anywhere to find out what it is, I presume it is a shunt or a diode? I have a diode from a Ford fusebox but it fits in either way so no good.
Everything seems to work ok but obviously I want to replace what I lost (have searched everywhere but its lost in the depths of the engine bay).
I've trawled the web, including on here, for any info but cant find out any info on what goes in this slot, every other image of an Espace (or Laguna 2 as its the same) fusebox has this slot empty and no amount of googling can give me any info, does anyone know what goes there?

Currently in stevedohc16v's garage:
2004 Espace 3.0DCi. 2010 Grand Scenic 1.5 DCi

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Fuse box component