Russell,
Have you looked through old postings in this forum? This topic has been covered several times in the last 3-4 months (lots of opinions and names of sources).
It depends on if you want stock (or close to stock/original) wiring, or if you want wiring for a wide variety of modern accessories (like A/C, electronic gauges, etc).
Classic Truck Parts and Chevy Duty have a variety of harnesses. The Chevy Duty "standard" harness is inexpensive, color coded, and quite well-made.
Tim
