2008 g35x 12 volts + at the bcm?

Is the battery not an option?  Why take a chance on accidentally tagging a 12volt output wire of the BCM that may be limited in current, and taking out the BCM.   

What kind of automatic doorlock module? I've seen a handmade module for sale online (KPierson I think?) that locks the doors when you drop the car into gear, or when you speed up. Is that it? That should take almost no current at all. Anyway, at the BCM in the kick panel, there are several plugs with dozens of small wires in them. There's another plug, however, with only three pins. Two medium size wires, and one larger one......WHITE/ black I believe. I use that heavy wire for my power source for remote start in all my Nissan/Infiniti remote starters.   The remote starter for that car probably draws a good 1-2 amps. If that doesn't hurt anything, I'm sure your doorlock module will be fine. Obviously, if the module you're installing doesn't have its own fuse on the harness, you should add an inline fuse, very close to where you tap for power. That way, if your wire shorts out to something, your fuse will blow and your module will of course stop working, but the car will continue to run.