Tony,
Our 427 harness contains over thirty different wire color/gages, more than twenty different wire terminations and takes about 10 hours to fabricate on several wiring boards - when done in runs of 5 to 10.
More power to Tommy for his frugality, but I suspect he uses only a couple of colors or gets his wire for free.
How much is your time worth? Figure on spending 15-20 hours on your first harness.
If you know what you're doing...
