What do you mean by electronic box?
If you mean ECU then it`s on the near side, under the plastic sections by the screen, in between the engine comp and the car. The covers are easy to pop out, then the plastic ECU box top has about 3 or 4 clips to un clip it.

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X5 3.0D 2003
Mods:
Webasto telestart remote kit
Aluminium running boards
Tv in motion & Aux input lead, Ice>ink to Ipod 3g.
DVD rear headrest screens and dvd sytem integrated in to main tv system via aux lead (watch tv or dvd in front and back)
Homelink Gate Opener, Chrome Grille Kit, chrome tailgate handle, Chrome Guage Rings, Tunit V-CR 086
Standard:
Bluetooth, comms pack, sat nav, sports pack, sports seats, dimming mirror, electric folding mirrors, memory seats, heated seats.