Clean engine bay, hiding harness ??

[withamc]

I do have electrical experience (I'm an electrical engineer), however, not having done this before I am looking for some guidance. I'm sure many who have done this weren't born with the knowledge.
Specifically:
Do you pull the harness back and feed it through the fender near the firewall? Do you leave the harness running along the firewall or do you find somewhere to tuck that away as well? Do you cut and splice (I would probably solder and shrink-wrap, but you get the point), and if so, what? Obviously you can't put some items behind the fender, but I'm sure the solenoid will fit. What else?
I'm not looking for step by step instructions, but some guidelines would be nice.
Thanks,
Chris