I installed my Whelen system by the book, best I remember.  I wired the 12V to the power supply with 14 AWG wire, and a separate 14 AWG ground wire from the case.  I used a 4 pin Molex connector where I cut the wire running to the tail so I could pass the shield through the connector.  I didn't cut the wires running from the wings.  I just fished them through the fuselage to my power supply.  The idea was to eliminate the two extra connectors which could be a source of noise.  The shields have a ring terminals at the power supply and are attached to the case where the 14 AWG ground wire is attached.  My system is quiet in my ES.  The power supply is under the pilot's seat.