On the cheap end of the scale, there's a $100 harness available from Chevy Duty. It's a vinyl-coated replica of the OEM cloth harness, nothing more. If you have accessories you'll have to tap into a hot lead and wire them separately. The harness itself doesn't care how many cylinders you've got, and the kit comes with a 12v (internal reg) alternator plug. The installation is brutally simple; follow the colors and match the numbers.
If you have a bunch of 12v accessories, you may want to opt for the more elaborate (ergo, more expensive) harnesses that already have auxiliary leads and a fuseblock. Shop around various vendors, and find something that matches your budget, power requirements, and skill level.
I had the basic harness installed in one day. Had I known it was a $500 job, I would have gone slower and used more 4-letter words!
