This is a question we get all the time when doing an engine conversion in the Z32 300ZX, both NA and TT. From the factory Nissan installed a Fuel Pump Control Module (FPCM, sometimes referred to as an FPCU). This module serves a single purpose, to vary the voltage to the fuel pump to reduce the pump speed at low load and idle. However, even saying the module varies pump voltage isn't a technically correct statement. Take a look at this wiring diagram: (Click for full size, will open a new window)
So you can see here that 12V power to the fuel pump is actually a constant 12V. This signal is uninterrupted by the FPCM. The Orange wire gets power from the fuse box and once switched sends it directly to the fuel pump. The FPCM actually comes into play on the ground side of the pump. Why? Because the FPCM is actually a variable resistor that increases resistance to ground when commanded by the ECU. If the FPCM gets no signal from the ECU, the fuel pump gets a zero resistance ground (Translation = Full Pump Speed). When the ECU sends a ground signal to the FPCM over the Purple and/or Black/Pink wires the FPCM increases the resistance which in turn lowers the pump speed.
Essentially, you need to do nothing with the FPCM when doing an engine swap. If you want to remove it for your own peace of mind, just put the White wire (Brown on diagram) at the FPCM connector directly to ground and remove the unit completely. Again, this is not necessary, but we know how some folks can be.