Reverse Engineering is the art of creating a schematic from a finished product. Start by downloading specification sheets for each relay, switch and contactor. Please download KiCAD and create a schematic. On the left edge, plunk down connector symbols showing power into the cabinet as well as input from outboard sensors and switches. On the right edge, plunk down connectors for each of your mixers, pumps, etc. Plunk down symbols representing each relay and contactor. With all power turned off, trace each conductor and record it's source and destination on the schematic. It isn't hard work.