They didn't want to make it too easy.
First thing you want to check is if there is a voltage increase at the battery when you plug into shore power. If there is, the converter is putting out. As the battery charges you should see an increase in the voltage that could go up to about 13.6 volts. If you aren't seeing any action, check the converter for fuses that guard against reverse polarity. One or both of them may be fried. Make sure you unplug from shore power and disconnect the battery when checking those.