I used American Autowire. Great tech support, and supper easy to follow instructions with wiring set up in packets per electric system of car. Also you don't have extra wires hanging out of the harness, as in this kit you connect and wire what you need. If later you decide to add, no problem just pull out the wiring package for that system! It really does take the guess work out of it!
American Autowire: Wiring Harnesses, Accessories, & Parts for GM Restoration, Modified Restoration & Custom Street Rod