Stu,
This may not help much, but;
The literal translation is "Electric Parts"

The local Japanese Petrolheads think it must be for accessories that require a permanent live because its attached to the battery terminal, so it might be an alarm, immobiliser, aftermarket stereo or something.
I'll also take it to the nearby Nismo place and ask for more info asap.
It might also be worth a quick phone call to ProSpec or Middlehursts, who are usually happy to help.