Where is the Black Box in a 2002 Mercury Sable 3.0 L V6?

I am not sure what you mean by "black box." There was never any kind of tracking module, separate recording device, or anything like that from the factory on this car. I have heard that there are things that only engineers can access in the memory of the air bag module, is that what you mean? The air bag module is located under the center of the dash, but it's not like you can, or would want to remove it. Here is the list of all the modules in the module communication network on a 2002 Sable: Powertrain Control Module(PCM), Generic Electronic Module(GEM), Restraints Control Module or air bag module(RCM), Anti-lock Brakes Control Module(ABS), and Remote Climate Control Module(RCC). That is all the modules that communicate on both the Standard Corporate Protocol(SCP) and ISO9141 networks on that car. On the 2002 Sable, They weren't using a Contoller Area Network(CAN) yet, so there isn't another network, or modules. If someone installed some other device after the car was sold, then there is no telling where you would find that.