In a High Performance Automotive and Aviation Applications Solder Joints are frowned upon because as you experienced;
1) Solder Joints fail in High Vibration applications where heat cycling and vibrations degrade the Soldered Joint. Soldered VDC Joints in these applications usually fail near the junction of the end of the Soldered Wire and transition back to Bare Wire.
There are some new metallurgically-improved solder, (referred to as LF-C2 Alloy), being used as an improvement for SAE, (but I still prefer Molex and similar high quality Crimp connectors vs Solder).
From Dennis Overholser Owner/Inventor of Painless Performance, (manufacturer of wiring harnesses and looms): :
“I have a saying I use in my seminars about soldering, Soldering is fantastic ... in televisions because they never move and encounter no vibration. In a typical OE harness, there are no soldered joints. Crimp terminals allow the wires to flex and prevents them from breaking. Soldering can cause the wire to become brittle and break.”
