Could be the shore power inlet on the side of the RV. Have had one of those wires come loose.
Take it one step at a time. Pedestal OK, plug in shorepower cable but do not plug into unit. Check for voltage at connector to unit. OK? Turn pedestal off & plug into unit. Turn pedestal on. If breaker trips on pedestal unplug & remove shorepower inlet. Look for loose wires or burnt wires. All OK? disconnect wires at incoming side of transfer switch. Check voltage at wires. OK? Reconnect inlet side & disconnect output side of transfer switch. Check voltage at output connections.
By now you have probably found the problem in either the female connector of the shorepower cable, the shorepower inlet or the transfer switch.
It takes time but methodical steps will reveal the source of the problem.