I'll through out one other thought. I see you are converting to 12V. If you get the 6V harness, the wires will be large diameter because they carry more current. That's what I did and 'if' I ever convert to 12V, the 6V harness will work fine.

BTW, I used the classic harness for $150 with no issues. Good luck

David Gilmore
Stovebolt Pictures
Paint progress
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1950 Chevy 3600