Everybody is almost correct (no, I am not a lawyer).

 

Some connections will be soldered - Microphone and headset jacks, D-subs that come soldered from a component manufacturer where you want to add a wire, etc.

 

Some connectors are crimped, such as the fast-ons used to connect to the gear-locked micro-switches.

 

Some fancy plug to socket connectors are best served by gold pins crimped with fancy tools.

 

Some less important connections may be satisfied with simple Molex connectors and crimped pins.

 

Some connections are done with crimped and/or soldered terminals, like those to circuit breakers.

 

Some connectors are insulated, some connections have shrink tubing affixed.

 

Some terminations are ring, some fast-on and some soldered if rigid.

 

What is common to the success (other than cleanliness, good tools, use of pookie, etc.) of any of these connections is their support in an environment of constant vibration.  In other words, wires from terminals and connectors must be supported, sometimes in bundles, to reduce the effect of vibration.  Soldered connections most often fail where the solder ends and the vibration work hardens and finally breaks the wire - The same can happen to a crimped connector without support (some is provided by heat shrink).

 

Perhaps reading some of the material at  http://www.aeroelectric.com/articles.html  can help choose how to make terminations.