What are the pros and cons to this wiring system? Is it really painless? Will it handle all the electrical goodies of this decade as well as all the standard stuff of a 1965 deluxe GT (rally-pac, fog lites etc...)?
They have new harnesses that are essentially OEM replacements, you know with the plugs and everything wrapped and bundled.
They also sell "universal" harnesses for MUCH less money that require you do do all the connecting and such. Do not underestimate how tough a universal kit is to install, I did.
any of the universal kits make things much easier to rewire a vehicle than in the past, as you have a prewired fuse box. that was always the worst part about rewiring. to say that any universal kit is painless though, is misleading to a point. you still have to make your wire runs, terminate the ends, etc. the custom harnesses are much easier to use, but also much more expensive. it will depend on how much patience you have for wiring a car. if you have little, then get the custom harness and save yourself many headaches. if on the other hand you like following your own path, and prefer to wire the car as you like, then the universal harnesses are just fine. i plan on using a universal harness when my mustang gets rewired.
I just completed re-wiring using the Painless 65 harness. I would recommend it. It has a couple of extra relays for running new accessories. My only complaints are that it isn't clear on the wiper motor if you don't have a motor with the original connector and it isn't clear on how to connect the 2-speed heater fan switch.