Instead of solder and heat shrink, you could use THESE for butt connections. One problem with soldering is that the wire can break right next to the soldered (rigid) part and the flexible part. If you're using crimped connectors, get a GOOD crimper tool. Soldering isn't really necessary with a good crimp.

Kevin
1951 Chevy 3100 work truck
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1929 Ford pickup restored from the ground up. | 1929 Ford Special Coupe (First car)
Busting rust since the mid-60's
If you're smart enough to take it apart, you darn well better be smart enough to put it back together.