BudW:
Soldering connections is NOT RECOMMENDED for automotive wiring. Crimped connectors is the way to go. I know it doesn't sound logical, and probably goes against everything that seems logical, but it is the truth. Use of heat shrink is optional, and a good idea, even on crimped connections. There are crimped connectors that already have the insulators made of a heat shrinkable material that are an alternative. Soldering is not a reliable mechanical connection method, it is an electrical connection method. There is an industry standard by a body called the IPC, and the standard is IPC-610D (I think it is D, it may have moved to E or F by now).
Solder connections will crack under the stress of vibration and rapid temperature changes, pretty much the conditions present in automotive environments. There are dozens of years of research in the electronics industry regarding solder joint cracking, not just of cable connections, but of printed circuit board connections as well. Important generally, critical in military and aerospace (probably the only two areas that see harsher environments than automotive).
Crimped connections are not just a physical smashing of two metals together. In a properly made crimped connection, the metal of the connector actually cold flows around the wire, almost becoming fused with the copper conductor. The metal used in crimped connectors is a specific alloy, chosen exactly for this purpose. The other part, which most people do not consider, is that the pressure used to compress the connector must be pretty exact. I know that in the automotive repair industry, it is common to use those sheet metal crimper tools, usually that have a stripper as well. It is not what is done in the electronics industry. The crimps are made with either a controlled cycle hand tool (it has a ratcheting action, when you start to crimp. you must complete the crimp with the correct pressure before the tool will release), or dedicated crimping machines, mostly electrical, but sometimes also with added pneumatic elements in addition. Whereas the crimps made by the sheet metal tools are just a single indented point, the crimps of controlled cycle and dedicated tools are sort of rectangular, and flat. The controlled cycle hand tools are expensive (for good ones), and that is why they are not used by many in the automotive repair business.
It is easy to see the truth of this. In any factory wiring, try to find a solder joint. Bet you can't. If you do the same to military or aerospace equipment, any cable connections will be crimped, never soldered, for exactly the reasons cited above. if there was a way to make printed circuit boards without solder, they would have changed over a long time ago. Believe me, they have tried. As it is, cracked solder joints on printed circuit boards are a major reliability issue, even today (actually getting worse, as the use of no-lead solder mandated by environmental groups has resulted in increased solder joint failures). If you can find a correctly made crimped connector (look for a rectangular indentation) on a ring terminal, cut through the barrel of the connector. Even with the barrel completely cut through, you will have a hard time separating the copper strands from the metal of the barrel. It should also be noted that crimped terminals come in sizes to fit wires of specific gauges, and it is important to use the right size terminal for the wire gauge.
Not looking to start an argument, I am just trying to bring some facts to this.