Carl wrote the Perfect 12vdc troubleshooting flow chart:
https://www.montanaowners.com/forums...ad.php?t=86323
You are definitely on the right track. If you have voltage on one side of those red self-resetting circuit breakers (#1 & 2) but not on the other, it is bad.
Replace it with Blue Sea or Bussmann one.
BTW #2 is 50A. #1 is 30A.