I done one in mine ,,
little button on to the slam pannel , and i took the live of the rear lights , and stuck the Led strip lights to the under side of the plastic bits that hold your shelf up
Hi.
I have a 2001 Seicento Sporting. The contact strip on the boot cill that takes power to the rear wiper and heated rear window has a little plunger that triggers the boot light when the hatch is opened. Not all models have a rear wiper and so the contact strip may be different and the plunger may not be there. If you get hold of the correct strip then you can use the earth that runs through it to switch the light. To pick up a live I would have a probe around with a meter at the rear body loom or run a wire back to the door courtesy light feed maybe.
Make sure your wires are big enough to handle the current and your contacts are well crimped and tight. My contact strip had melted the earth contact into a blob stopping the wiper, hrw and boot light from working.