If you get the kit from Ford Racing, it includes the jumper wires to modify your stock harness. From the Ford Racing Website:
Mass Air Conversion Kits
MUSTANG KIT INCLUDES:
• EEC-IV mass air processor module assembly
• EEC-IV jumper wire harness
• Mass airflow sensor, hoses, clamps and brackets
• Easy to follow instructions
If you scrounge the individual parts yourself (MAF and computer), then you will also need a harness from a mass air car.
Pete