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One part (3C3z9d930aa) is the FICM wiring harness for an 03/early 04 model year engine. The other is for a late 04. To decide what one you need with your 04 model year, locate the ICP sensor.
Also
Ford part number 101.
ANY Ford part number is divided into three sections, the PREFIX (5C3Z), the BASE PART NUMBER (9F452) and then the SUFFIX (AA). On ANY Ford part number the PREFIX will ALWAYS end with a Z (some early Lincoln/Mercury model line specific parts used to end with a Y). If the prefix doesn't end with a Z, it is NOT a Ford part number. It is either a STAMPING number or ENGINEERING number.
The 03 harness has no 90* turns on the rear Ficm plugs. The 04+ one,, 90's outta the Ficm. Is funny how they box them,, they are bent the opposite way in the box than how they are installed.