Assuming you have a Xantrex: E03 is overload, press and hold the SELECT button for 2 seconds to disable the alarm but you will probably have to turn the inverter off to clear the alarm condition.
E03
Inverter Output Overload (or Short Circuit) Shutdown. Unit is being severely overloaded. Reduce the load.
If this fault occurs in shore power mode the unit must be reset. To reset, remove AC loads and turn inverter power off and
on.
Linear Mode
