summery of the passage below: which cable can i plug in a old disabled alarm's red led into so that it turns on when i turn off the car and turns off when i turn on the car?

EDIT: i own a 94 accord coupe.

...ok so im going to be installing a new stereo tomarrow, and i noticed something intresting tonight as i was setting up for the quick installation tomarrow, i found the old led light that went to the alarm system for the car before it was disabled, and i was wondering could i just splice the led into a power cable so it will stay on and make people think i have a alarm? ok so thats a dumb Q, i know i can do that but im wondering which cable will turn on the led when the car is off and turn off the led when the car is on... anyone know?