There are 2 ways to do it.

The easiest way, is to splice both the positive and negative wires to the parking light of the taillights. However, it will only be on when your parking lights are on, and will still be on when you close the trunk.

the 2nd and proper way, is to splice the positive wire to a constant power source. If you have an amp in the trunk, that is where I did it, if you have no power in the trunk, you will need to run the wire to the front.

For the negative wire, there is a black wire near the trunk latch that you can splice into. There's not a lot of room there, so be careful where you splice into.

once you do that, the light will turn on anytime the trunk is open, and will turn off when the trunk is closed.

have fun