Steve, in your description it seems like the things which work when only AC power is supplied run directly on the AC power, and the DC stuff is not
being supplied by a converter. Basic converters produce pretty rough DC power when no battery is connected, and that power might not work for Frederick's motors (furnace and water pump), but it would
work for lights... so I think it's time to look for a converter and see if there is one, and if it is turned on and working.
people: can anyone describe the location and appearance of the converter in a 1987 Scamp
13', and maybe hints for what switches, fuses, etc. need to be checked if it is not working?