LED on with interior lights

This is a simple project, but I still am unsure as to go about it. 

I want one LED light to turn on when the lights inside my car turn on triggered by opening the door, and they will turn off when the key is turned.

This already happens in the car, how do i tap into it?

i'm guessing that i need to find the relay that the door open sensors talk to and connect there - is that about right?

Well, it should stay on until the ignition is turned - just like the dome light does now.  Which is why I thought a simple way would be to wire it to the dome light

It is a 2001 Nissan Pathfinder

I'm assuming there is a relay somewhere that controls the lights, I'm just not too sure where to look

So I am looking for a wire that goes negative when the doors are opened.

Is it a relay that controls the lights and leaves them on until the ignition is turned? 

try this

The SECU (Smart Entrance Control Unit) is between the steering column and the fuse box. 

The driver door trigger is GREEN/ red in pin 29, the front passenger door is yellow in pin 40, and the rear door is RED / blue in pin 28.

thanks.  how will i keep the light on until the ignition is turned?  is this done inside the secu?