thanks, eggsample and your discovery.
anyway, i used the sd card metal housing for the ground, shortened the
wires and it's still not detected, turns out the problem was the sd card reader.
my usual sd card reader doesn't work on the 2ds.
of all my readers, only the Transcend 15-in-1 works.
2ds nand dump has the same size as the regular 3ds.
What is the color of the SD plug of your USB reader because I have noticed this :
Front
Back