That's the only way that I make wiring connections. And the blower motor was replaced either 2 or 3 resistors ago.
For reasons you stated. Failures have gotten further between since the motor was changed but still happening. I have been alternating it seems between both Warner and standard brand resistors.
I STILL this the problem is the terminals between the pigtail and resistor are too small. Not enough surface area for the amp load present. At work I see this alot since they came out with the super mini low profile fuses. I often have to relocate the fuel pump fuse on 09 and newer Ford trucks with these fuses to an unused hole in the fuse box meant for the larger series of fuse.
I replace with the same 20a in the larger series and have never had a comeback on that issue.
Ford even sells a "fuel pump fuse relocation kit" for $20&some....for this exact issue.
Likewise I'd like to find a blower resistor and matching pigtail with larger contacts that I can swap in.
Another thought, for the next couple days after the most recent one went bad I did smell hot electrical/plastic smell when I first turned the blower on but each time it subsided after a couple of minutes.