The same thing happened to me with my 2001 trailer. The problem was the connection where the shore power cord connected to the trailer. It was in a junction box and the connections were with twist on wire connectors. One of the wire connectors had worked loose and the connection was bad and the wires had burned back about one inch.
I cut the wire back and reconnected with a new twist on connector and wrapped the connection with electrical tape so it would not come loose again.
I learned in my boating days that twist connectors are a bad idea in vibrating environments. I should have used a more robust connection but didn't have time.
