[rohrmann]

On our rig, the breaker that feeds the hydraulic pump is the same one that feeds the 12 volts to the panel, so if yours is the same, when the breaker is open, not only will you not have power to the hydraulic pump but the batteries are not feeding the panel either. Once you connect shore power, the converter is powered and is energizing the 12 volt side of the panel, so that's why you have 12 volts once you are on shore power.