The 12V system won't work off the battery. When plugged in to 110V, the interior lights and everything 12V works, so the converter must work. The battery has 12.56V (when not plugged in). I checked the battery voltage going into the converter, 12.56. Voltage at the top fuse (15A) is 12.56. There is no voltage at the other 15 and 20 amp fuses. I checked the switch that cuts the power when the trailer is down (it's under the swing sink on this model). It is only reading 0.21 volts. My best guess is a poor ground connection somewhere, but why does it work through the converter? Why is there no voltage to the other fuses? Any ideas?