Add extra LED strip to interior boot/trunk light?

[MetroMPG]

Ah, interior light.

I would splice it to the wiring of the existing interior boot light, or to the bulb itself as you say.

You've done it before, so you realize there's a polarity requirement for the LED to work. Test before you solder.

Not sure which fuse it is. It'll be an "always" hot circuit, so probably not the cluster lights.