Car Wiring - Adding lights

[rawfuls]

A taad bit confused, need to start looking more into electrical systems.
Anywhoo, here is the bulldogsecurity page:
http://www.bulldogsecurity.com/diagr...4424&MakeID=26
and 'the12volt' (this is a 2000 Sportage, I'm a 2001 Sportage, but they appear to be the same).
http://www.the12volt.com/installbay/...tail/1249.html

In both cases it appears that they are switching the negative (yellow/green[-])

Where would I find the 12v lead and the ground to the door pin?

In other words, I'm tapping directly into the door switch (that black knobby thing, that pushes in/out for door)?