Ok so heres what I would do

Connect the ignition barrel to the BEM

Connect all earth and +12V lines to both the ignition barrel and BEM

Connect the BEM to the computer

Hide the BEM and ignition barrel (in "on" position) away under the dash or passenger seat.

That about it?

I'm assuming the courtesy light would be +12V

That's the theory. Practice I can't help with, as I haven't retrofitted EL gear into pre-EF/L car.

Good luck to you, and I guess people will start screaming for a doco, so take pics and stuff.

Yer will do, Not looking forward to this and frasers teasing doesnt help. This better be worth it. If i can get 600km to a tank after this mod I will be happy