Bruce,
Your assumptions are correct, but not quite complete. My suggestion is that you print out the following diagram and part number key, and laminate it for future reference. The wiring of the MFI and engine is identical to '73 models, and I recommend using the same color code for everything! A parts recycler might be able to supply an MFI engine compartment wiring harness.
http://www.pelicanparts.com/911/911_Parts/Electrical/911_electrical_1971_Part-2.jpg
http://www.pelicanparts.com/911/911_Parts/Electrical/911_electrical_1971_legend-2.jpg
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Warren Hall
1973 911S Targa