If you want to learn how to build a harness, start by getting the right tools.
You can get ratcheting crimpers
here for a very reasonable price. (Thanks again for the tip, Nep.

)
Here is a large list of dies to go with this
336 ratcheting crimper frame that can take either 236 or 336 series dies.
Dies that you're likely to find useful include
336-H,
236-2U, and
236-2C4.
On many of the die pages, you can click on the Data Sheet tab to see a diagram like this.

Scott