Sounds to me as though you are replacing the old system with a new one that has crossover net works internal to it. If the old system is completely gone and you are running new wire you will not need to do the mod. It is just for the stock system and basically builds a crossover( capacitor) to put power to the woofers and keep or limit power or frequencies to the door speakers which are mid range. This is what I understand is happenning, or something very close.