Mine has a circuit breaker in the wire between the battery and the converter. When that is open the converter powers all the 12v stuff but not much works on battery alone. The same is true if the battery disconnect switch is set to disconnect. The above circuit breaker is under the bed, on the passengers side. If its not the CB or the battery disconnect, you may have a fuse near the battery in the same wire. The generator starter power comes directly off the battery.
You probably have a Magnetek or Parallax 73xx converter. I don't believe it has the reverse polarity fuses.