replace the efi harness to convert to mass air easy? This makes no sense, is completely not required at all. You need one harness from the computer to the meter, readily available and simple to install. Buy the book "how to modify your fuel injected ford". It has wiring diagrams that are simple to understand and easy to read. compare the speed density schematic to the mass air one, and you will see the only differences.
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1993 GT/AOD
'93 Mustang GT