For those of you who have wired your cars from scratch, where did you buy all of the singular components (wire, fuse blocks, bus bars, terminals, relays, etc.)? Is there any source to stay away from?

After a minor wiring issue / fire in the pits, I ended up using 2 Painless kits. 1 is a stock replacement and the other kit is for the race stuff (W/pump, Fuel Pump, Fans, Ign, data Etc). I upgraded to weather proof connectors where the current would allow and H/D connectors where more current is needed. Most of the extra stuff you mention, I bought off Ebay. I got burned on a couple of items and didn't use them but if you go through a reputable vendor you will be OK. I also switched all the lamps (Bar the headlamps) to LED's and ran an earth loop round the car. It made a big difference, especially on starting. The car has all the stock stuff working and the correct size cables, current capacity and fuses for the "extra's". Race only ? I would just use a race kit with the correct number of circuits (plus a couple of extra's for future), that you need.
Edit: I've added a couple of 'phone pics of the boot (Trunk ) area (All I have).

I like the relay and fuse boards from leash electronics. Wire for relay triggers sensors etc (20-22ga) I use wire from my EFI supplier because it is labeled, for any load carrying wire I just use a hodge podge of stuff I bought from a customer who was closing down. For Crimp connectors I use QuickCable, because we are a vendor at work, I like the non insulated stuff then skrink wrap it. For weatherpack and metripack stuff I use ebay, amazon.

If I ever win the lottery I will have a room full of wiring supplies because I never seem to have the right thing lol, that and a wall of nut and bolt hardware lol.

https://www.racedigitaldelay.com/switch-megapanel.php

I FINALLY gutted my rats nest of 20+ years and went with this kit….. no complaints and it was readily available and they were able to answer all my questions. Even went back and purchased their shift timer from them. On my bus bars I ordered some through Amazon.

My stuff all came separate. To me a relay serves no purpose if its not close to the device. The last two I wired started with a used ARC box. Relays were placed near the device they were intended to control. Colors for wire were selected. All battery feeds are red, ignition feeds are pink, grounds black. Take time to come up with the routing. Once the devices are mounted in the final location the final colors were chosen and run from the device back to the arc or junction strip. Unseen wire bundles were zip tied instead of taped. Easier diagnosis in the future. Where harnesses were visible they were covered with expandable braid (Chinese finger). It takes time and may not be as fancy as store bought. But a very functional system can be achived.
Doug

A good marine supply store has a lot of quality individual components, wiring and connectors available, due to Coast guard regulations for it's intended environment. This helps if you can build your own systems or redesign or repair. Of course you will probably pay more, but sometimes when you need stuff, being immediately available is a big plus. They generally have more and better materials than the average auto parts stores. No plug and play kits for cars though. Just the ability to see what you are actually getting, vs. choosing from a picture or someone's description. Bill

Individual components we use Waytek or Delcity for wiring, connectors, mega fuses etc. I reallly like the XS Power liteweight battery cable and it has worked well for us. I use Duetch connectors these days on most stuff but have used weather pak in the past. We just rewired our new dragster and used a K&R relay panel and switch panel. Nice stuff for sure. My new project is getting Speedwire like the last couple have. Those are the two we use these days on most stuff. But have used Spaghetti Mendors and Leash products as well for certain thing.

Devin Vanderhoof on YouTube has some excellent videos on wiring cars, relays, different connector styles and wire. Racespeconline.com and Del city wire are great sources for supplies and tooling.

I have bought a lot off Amazon , BUT read reviews and be careful , some of it is decent , some of it is junk

Thanks guys. Lots of good tips. I'm excited to get started on this project. It'll be a great learning experience for sure.

I found Clips and fasteners on Amazon when I just needed 25 count of Packard 56 terminals. I like the quality of the tin plated terminals, and price was not too bad for small order.
https://www.clipsandfasteners.com/O-E-M-Terminals-Shells-s/259.htm

Waytek wire carries name brand (like 3M) terminal connectors, heat shrink, wire, switches.
I mention this because many of the cheap off-shore no name brand terminals are junk. Friend gave me a harbor freight ring terminal kit, and the metal was so thin, you could not get a good crimp on the wire, like trying to crimp tinfoil over a wire.

There are a bunch of places to for GXL/TXL wire, like wirebarn.com

WireCare.com carries Tefzel wire if your going real high end stuff.

The Packard 56 series is what most of the factory connectors are, but they are not sealed from environment.

Weather pack connectors are sealed, but bulky, and really don't like being connected and disconnected more than a few times, but they are fairly inexpensive.

Metri-pack connectors are more of what newer cars use. Usually smaller sized shells, and pretty easy to connect/disconnect. usually price is good too.

Deutsch connectors are premium. The pin/socket terminals are good for multiple connect / disconnect cycles. Connectors (and pin/socket terminals) are more expensive, and the terminals should be crimped with the correct type DMC crimper tool that can cost several hundred dollars.
The circular autosport connectors are similar to mil standard 38999 connectors.

The painless kit I bought with relay board had some shortcomings where certain circuits didn't have adequate wire gage. I personally wounldn't use the touchpanel switching some kits utilize. Also weatherpack connectors are lighter gage/lower amp than I care to use. I pieced and patched my vehicle with several differnt sources but then, I had a good wiring guy handy to reference...DVW!