. No returns, no instructions, no free shipping and same price or more. No advantage whatsoever.
Been there, done both. Buying one is the way to go.
Alternate opinion: There are plenty of reasons to build it yourself.
If you are doing a single vehicle, the cost to buy the supplies is comparable to a Painless or Speedway harness. If you do much electrical work, the extra wire you will have left over is good for all kinds of things. If you plan to wire more than one vehicle, the savings are fairly substantial over the high quality off-the-shelf setups.
Building your own harness lets you route things exactly how you want them, combine or separate fuses as desired, select from a wide variety of shapes and styles of fuse blocks to fit your physical location and/or cosmetic desires. You can also select a fuse block that uses the style of fuses you prefer (whatever that is). You can select your own wire sizes on a per-circuit basis to match the intended use as well.
As far as instructions go, that is what a wiring diagram is for. These trucks are pretty darn simple.
Putting the ends on the wires takes a few seconds each. The greatest majority of fuse blocks you can buy have pins that your crimp on and slip into the fuse block, so no additional tools are needed over what you already need for the other ends of the wires.
That said, I do agree with a number of the points made above.
Making your own harness from scratch does take more time and effort.
You do have to read the wiring diagram and hook things up properly, but if you are not capable of that, you probably should not be doing any wiring changes.
Having wires labelled along the length is fine. Painless started that and pushed it as a big deal. I have never been particularly enamoured with it because it locks you even further into hooking everything up exactly the way they intended. Some people really like it as a feature, your mileage may vary.
If you are not planning to do anything different than the last 2500 people who rewired a truck, any of the solutions will probably work fine for you. You trade effort for cost up to a point. Based on your intial post, this sounds like a pretty simple wiring job.
The smaller harnesses (12-14 circuit) will probably meet your needs and be cheaper than a 21+.
