just had a look at my 5dr and I don't have any sort of exposed plugs in that area.
not even shown on the nissan4u wiring
http://nissan4u.com/parts/micra/er_k11e/1995_1/type_9/body_electrical/wiring/illustration_3/
do 3dr have any rear speakers in the rear side plastic panel or is it only on the parcel shelf? could be a reserved plug cos different models share the same loom. best test it with a meter
