I did a bit more checking on the internet and the following site does an excellent job showing the proper way to solder connections splicing wires- right and wrong. Of interest, Toyota Motor company in their shop manual recommends using both a barrel crimp and solder for wire splices.
The box crimp connections used by most shops to splice connections don't make a strong reliable connection.
There's some misconceptions on that web site. The reason they gave for not using wire nuts is one. Wire nuts work well in an environment where moristure is unlikely. My Scamp
came from the factory with some connectes using wire nuts. I installed a propane
detector and used wire nuts. Proper size and properly tightened they won't work loose.
Soldering - As I stated before to get a good solder joint takes a lot of practice, other wise it's hit and miss. You might do ok, you might not. The second thing the wire becomes brittle, I think I said this before, at the ends of the solder flow. As a professional that works electrical
stuff every day the most common failure is solderjoints. Any wiring solder joint where the wires can and do move will fail, it's a matter of when.
As for the practice of soldering crimp joints. I know that one truck manufacturer does that. However it's not a good practice for several reasons. The reason they can get away with is the people doing the soldering are professionals when thousands of solder connection in resume.
As stated other places a proper crimp connection is the most reliable, tests have proven that over and over and over, etc. Also somebody mentioned a couple types of crimpers. The ones that require you to get enough crimp before the it will release are best. In my office I probably have 6 or 8 different crimping tools. None will allow an under crimp or an over crimp. [b]The crimp connector has to be the right size for the wire you're using. This is one mistake often made. Usually a connector that's made for a larger wire.
Back to solder connections for a second. You can improve the life of a solder connection by using 2 layers of shrink tubing, with one layer being shorter than the other. The short piece should extend at least 1" beyond the solder connection on each end the long at least 2". This will provide some strain relief so the joint won't break as soon as it would otherwise.