Thanks to Will’s comment that the fuse I thought was still good might actually be the bad one, I started to make progress on my electrical problem. For one thing, each time I tried to replace the fuse, the new one would blow.

Amazingly enough, I knew how to troubleshoot one step further: disconnect individual components of that circuit until I found the one that was causing a short. I also knew right away where the problem was and started there: the new 12V outlet. I disconnected it and tried one last time to replace the fuse that kept blowing. Not only did the fuse not blow this time, everything else started working just fine. Yay, I have a fridge again!

I’m going to give up on that 12V outlet and start from scratch with a new one.