I had #4 speed fail 6 months ago and when #3 failed a few weeks ago I decided it was time to do as you did. Soldering is the best solution. But when I started digging into it I discovered it is harder than it looks. Looking closer at your picture, you obviously trimmed the plastic on the resistor to get to the terminals. Next your picture shows plenty of wire but the factory harness has very little wire outside the harness so that probably had to be stripped back also. The wiretie would indicate that also since the factory wiring harness tape would suffice.
But the final straw for me was that I found all of the resistor terminals were good and the issue was a burned off connector terminal for #4 and a loose connector for #3. I cleaned it all up and put it back together. #4 still doesn't work because it was burned completely off but #3 is working again and the rest were fine. I have found the connector for less than $10 delivered and that will be my solution unless the resistor plugs burn off.
I like your idea and I think it would be a more permanent solution but it is a bit more work that it appears from your 2 photos and a lot more than just replacing the connector if that is all that is wrong.
