Matt, I’ve been building my own harnesses for many years. I personally find it enjoyable and relaxing. When I have a project under construction, I usually start looking at the part store wiring section for the different color and gauge wiring and pick things up a few items at a time to spread the cost out and try and make sure I have I need when I get to that part of the project.

I few things I learned along the way that might be helpful:

List out your circuits/accessories.

When you start building the harness, draw your wiring diagram as you go, making sure you include wire color and gauge. I usually draw each circuit in as I complete each one.

On complicated circuits (stereo, ignition, cruise control), make a separate wiring diagram which will be easier to read if necessary.

Add a couple of extra un-terminated circuits to the rear of the car and engine compartment in case you want to add something later on.

Protect with headlight circuit with a circuit breaker rather than a fuse.

I usually run a Ford Solenoid (even with GM and Chrysler starters) in a convenient location …….it makes it a lot easier to hook a remote starter switch and if you ever have to remove the starter you only have the main cable to remove from the starter.

It’s a lot cheaper to buy the terminals and connectors in bulk than the small packages and if you do your own wiring they do eventually all get used up.