My 20+ year old Kenmore (110.66712694) stopped heating, so I took it apart and tested all components with my multimeter (all seem to pass). However, I noticed the wire going to the cycling thermostat was in really bad shape, and as soon as I touched it, it started falling apart.

I have a ratcheting crimp tool, but I haven't been able to find the proper size spade terminal connector, and I'm not sure I can trust some cheap assortment kit from Amazon. Any recommendations would be really appreciated.

I also wonder if the rest of the wiring harness is safe considering I see corrosion on the failed wire (but visually everything else looks ok). Doesn't look like a replacement wiring harness is available anymore.

I do have a new heating element and thermostat, but do wonder how I can protect myself from this type of failure since a fuse isn't going to stop this potentially catastrophic event.

Over the years and quite a few electric dryers back I have seen the exact same problem at these connections . The FASTON type of connector used is a larger one than is normally available in wiring kits. Most of the wiring kits have a .25" type of female connector to fit the corresponding .25" male blade. The ideal connector to use is a slightly larger one and some electrical repair shops may have these but you will have to search really hard to find a shop that has some.. I have one or two but I guard them since they are hard to find.!!! I have also done a repair3Y7QSnsd using the .25"size FASTON but will not put it in print since it is not an accepted safe practice.

Generally speaking, a properly sized hi-temp uninsulated terminal will work just fine.