No DC Power in Pop-Up Trailer

Today my 1998 Coleman Mesa pop-up trailer's lights (and everything that used dc) didn't work while the camper was plugged into shore power. When the battery is connected, the lights turn back on (shore power unplugged). But when plugged into shore power (no battery), everything except for the 120 volt outlets, didn't work. I checked the breakers and fuses, all is good. Could this be caused by a stuck relay switch in the converter?
Thanks so much,
Alex L.