The pressure switch in your spa controls the water pressure in your spa. The pressure switch harness is a replacement part for the original pressure switch harness that allows the pressure switch to be connected to the controls of your spa.
The Master Spas Freeze Plug Kit contains a plug set that works on most spa pumps. This can be loosened to drain any trapped fluid within your pump. Replacing a broken pump ? Make sure to get new freeze plugs as well.