I purchased your cable and now I change for a mobo without firewire.
No. You need to connect any ground from the motherboard to pin 3/4 on the firewire connector.
From the pdf
-If your motherboard does not have integrated firewire on-board, you will need to connect the pin 4 from the firewire (FW GND) connector to the -GND on the power button connector.
My question: do I need to connect only pin 4 to ground, or pin 3 AND pin 4 ?
EDIT: just pin 4