I don't know about you but I'm perfectly happy fabricating chassis, welding and doing body and paintwork, and physically putting a car together, but I've always left the wiring in my projects to someone else. Of course, having a good friend who owned an auto-electrical company, and who was always happy to trade bodywork favors for wiring, meant I never really had to worry much, but he's on the other side of the planet now and so when it came time to wire my '46 I decided to bite the bullet and tackle the job myself. My cars are usually pretty basic with not much in the way of accessories-- not even a radio--so I figured a simple wiring harness with the minimum of circuits would work best for someone who'd never wired a car before.
After a little research, EZ Wiring's 12-circuit harness looked perfect for my needs, so I called 'em up and ordered one. However, the project then somehow became relegated to the back burner for a couple of years, and it wasn't until I decided to drive the truck to Bonneville last year that I actually dug out the still-boxed kit and took the plunge. The installation was pretty straightforward and pain-free, if you disregard the couple of errors made by me and the need to fabricate a mount for the fuse box.
Methodically following the instructions and breaking the job down into sections like engine harness, front of car, rear of car, and interior certainly made things easier, especially as I didn't unravel one section's wires until I'd completed the last. That way there weren't a whole bunch of wires all over the place. With the exception of the turn signal switch, everything worked fine the first time. Somewhat pleased with myself, I'll certainly tackle the wiring in the Project '49 Chevy myself, and may even move on to doing my own upholstery next. Er, maybe.