I just purchased a 1977 Dodge Monaco Motorhome. Everything works well except for the 12 volt system. I cannot get anything to work off of 12 volt. Everything works fine when plugged in to electric, but if I unplug and start it up I get nothing. No lights, tv, refrigerator etc. The guy told me that it worked fine the morning before I showed up, could be a lie I don't really know.He tinkered with it but could not get them to work. So hopefully it is an easy fix that I am missing somewhere. The light on the ceiling between the driver and passenger seat will turn on when the door is opened which tells me it is getting 12 volt power. If I shut the door it goes off and I cannot get it to come back on with the switch. I am open for suggestions at this point. It doesn't make sense to me that the light works when the door is open but not when it is switched on manually with the door closed. Any ideas????