Which route should I take with wiring on my swap. I will be running a Holley setup with a 4L80. Do I yank the factory Mustang harness completely and start from scratch (using aftermarket harness), or is it better to leave the factory harness and splice each piece into it? I am assuming Painless, etc.. can make me a full harness ready to go?? What issues could I run into going either route?