Got home to look at a schematic. From what I see SS72 is correct. I don't see the option gage wires in the idiot light harness, only the idiot light wires. Things like a voltmeter and tach have nothing to tie to.
These later harnesses have a large plug in connector that fits into the wiring board. That's part of the dash harness. If you want to do this you probably will need another dash harness and engine harness from a gage car. Best I can see from the books I have. I also did a search on replacement harnesses. M & H doesn't produce one for the 79 Elky.
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