Chrysler didn't use solder on the fusible link terminals, nor on any other crimp in the entire wiring harness, and neither did/does any other car manufacturer that I know of.

Solder is very useful for plumbing and printed circuit boards (I used to work in a PCB factory, through-hole soldering terminal blocks into about 1,000 PCBs a night, for 2 years, and I still do a lot of soldering at home when fixing old PCBs), but it isn't so great for car wiring. It will do in a pinch, but a proper crimp is superior.

A proper crimp is airtight, so the wire within the crimp can not corrode, and it is also still flexible. Corrosion isn't really an issue with a soldered joint either, but it is comparatively brittle, which is a bad thing in a high-motion, high-vibration environment which is subjected to many cycles of hot and cold. Cars use multi-strand wiring because of this (rather than solid core like in houses, where there is no motion), and using solder defeats the purpose of that (solder will crack a lot easier than even solid core wire). Every solder joint you add is a weak (brittle) link in the harness. You can see this for yourself by simply tinning a section of wire and then flexing it several times. It won't take long to crack.

A lot of repairs I do to old PCBs consist of re-soldering old cracked solder joints, especially on the chassis of old CRT monitors (i.e., from 1980s video arcade machines), and those aren't even usually subjected to significant motion/vibration. The cracking is mainly due to many hot and cold cycles over a long period of time.