Converter problem or something else?

I have a weird problem and can't seem to figure it out. When I unplug my rv from shore power none of my 12v system (lights, slide, etc.) works. The battery is brand new! I have checked all fuses (good) and have checked the converter ( Intelli-Power PD 9160) and come up with mixed results. I unplug the converter from power and remove the hot wire from the battery and plug back into power. When I first check voltage it reads around 14v then after the initial reading it only reads small amounts in Mv. I checked the fuses on the controller also and they check good. ANY help will be greatly appreciated!