Outlets in travel trailer not working

Hi, we just bought our very first trailer. It's a 1983 Mallard 20 foot travel trailer. Got an old one to see if we would like taking care of a trailer. The man we bought it from had it parked for 3 years without moving it. We bought a brand new 12v battery and everything turned on as soon as we installed it. But the outlets didn't work. We tried plugging in a little radio to check the outlets and,,,nothing. The bathroom outlet has a ground and we pushed it and it clicked, but still nothing. I've checked everywhere for a manual,, impossible to find. The previous owner has no idea what could have happened. Help please.