What is a reasonable way to connect small wires?
For a good connection that can withstand lots of movement/bending, use:
- Solder
- Crimp terminals (either permanent "butt" connectors, or male and female terminals if you want to connect and disconnect)
- Screw terminals ("terminal block")
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(Image from wikipedia.org)
For a more temporary connection that is quick to add/remove: Use spring-loaded terminals
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For a hack that will work in a pinch but destined to eventually fail under light abuse: Twist the wires together and add wire nuts or tape.
(Image from cnc-plus.de)
This is all under the preface of "clear weather" as you had stated. Note that while weather can be "clear", hidden moisture in the air can still accelerate corrosion/rust over time, depending on the metals involved. Corrosion can lead to shorts or opens.
I would solder them and then use three section of shrink-tube. One around each wire and after that a third one to cover all of them.
But then I happen to have a drawer full of shrink tube of various sizes so I don't have to buy some...
Yes. Assuming these wires are not being moved or pulled apart, a rat-tail splice insulated by electrical tape is perfectly acceptable. However, if they are being pulled apart, you'll need something more.
You may very well get away with a western union splice with no solder if the wires are being lightly pulled apart, but this is risky so you should just apply solder anyway.