GC ignition key light wiring

[ScoobySam8]

Bought myself a jdm ignition key light for my GC, and now I need a little help wiring it up. I've figured out how it works by touching the wires on my car battery, but now I just don't know which wire to connect to

There's 3 wires: 1 connected to constant 12V (no problem), 1 connected to constant ground (no problem), and the last I am having trouble with. The last wire needs ground when the door is openned, then needs the ground to 'drop-out', or have a negative power draw, to light up then dim out after 10 secs after the door is closed. So...my question is, what can I connect this last wire to!? I've spend the last 30 mins in my car with a multi-meter trying to find a wire with 0V (when door is open) and -12V (when door is closed). And no, hooking up to the dome light doesn't seem to work (or you could explain to me how it can work )

Thanks for reading everyone, and I hope you guys can help me out.