Your got a short or cross connection going. Check the 7 way trailer side male plug. If it is a molded unit -is it damaged or deformed? If a replaceable type check the inside for lose connections or wire whiskers cross connecting.
Next stop would be the junction box on the trailer that the RV 7 way lead cord originates. Check for the same loose or cross connected situation... Beyond that it is a tedious one piece at a time troubleshooting process.
Don't think it is a "ground" only side problem as the circuit has to be energized from some source.
