Not saying this how you "should" do it but it worked for me.
I installed several LEDs in my Jeep and just tapped into the existing 2 wires for the interior lights, the ones under the dash. No fuss no muss, had'em done in mere minutes.
I also found LED's on Ebay that had the same socket as the factory bulbs which made it super easy for doing the interior door lights and dome lights.
This is a example
http://www.ebay.com/itm/Xenon-White-...7b7abb&vxp=mtr