You would need to tap into the ground wire there too, I am pretty sure that our door switches supply the ground and not the power.
I soldered leads off of the dome light bulb prongs, that way the lights were on any time the dome light was. Only issue i had here was that i had a lot of lights powered from there and was not getting much light output (i had 60+ LEDs powered from there) so i wound up installing a relay that was switched by the dome light. Only issue there was that when the dome light dims it drops to 6V so it made the relay freak out and it would buzz. The fix for that was some no-ox-id grease over the contacts inside the relay. It still buzzes but its barely audible now.