G'day mate,
not being a sparky of any description, I can't help, sorry. To help others help you though, it may pay to let them know what wheels you're driving as I'm guessing the circuitry will vary between models.
Would have bet the house on it being in one of the door switches though.
Have you downloaded the complete manual for your model? Follow the circuit in the electrical section because that will show everything which may be on the same 'line'.
'Cause I'm old and lazy and not quite with it, I'm not going to do that yet but I'd be a bit surprised to find the cigarette lighter is on the door circuit. Let's know what model and if it's a GU 3.0CRD I may be able to look it up for you.
Help is probably on the way though.
Good luck
Col