Are you looking for a place to do a custom retrofit job - say, from a s2000, TSX, or other car?
If not, most of the HID kits on the market are plug and play. The low beam kit I bought from SharpHID for my 07 WRX was plug and play (including the battery harness). It was obvious where to plug everything in and the only modification I had to do was to cut two little holes in the back of my plastic caps behind the low beam bulbs for the HID wires to feed through.
07 WRX (Albins 5MT + Blouch 20G)
Jorge Carrillo Tuned (365 whp/340 wtq)