It is so that you can run more boost than the stock MAP sensor can handle which is ~11.2 psi.

You need to wire it into the stock MAP sensor circuit and supply it with a post-throttle body vacuum source. You can then unplug your stock MAP sensor.

Keep in mind that once you do this, you will need a complete retune. All the maps will have to be scaled back accordingly since all the pressure voltages have now changed. That is the biggest reason why my 3.5 bar MAP sensor isn't hooked up yet.