I am NO Fiat electrical guru that is for sure. But I ran an electronics mfg plant for 25 years. The thing with crimps is that the system is always (as far as my experience) designed to carry at least the amperage of the underlying wire/conductor. No connector manufacturer wants their "faston" type connector to be the weak link in the chain. So soldering the crimps to increase current carrying capacity in theory is not necessary. But theory is often wrong in the real world. The crimps have to be good, made with the proper dies and force. And the underlying conductor has to be clean and uncorroded.
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For what it's worth.
In general aviation we are instructed and tested in the use of crimp connectors.
The crimped connection should be stronger than the wire itself when done properly.
The only soldering done in GA electrical is for the most part doe on the very fine wires involved in avionics. And usually on the bench.
The rest of the electrical system of an aircraft is connected with crimp connectors.