I think we've solved the problem. Upon arrival at the Millennium factory, they removed the tow bar from the Marathon to install it on the new coach and when wiring everything up, they found a total mess of wiring on the Lincoln. Wires which were to go to the battery were not hooked up properly. They started from scratch and now all of our lights are working properly for the first time. On the way down we discovered if we put the vehicle in "park" and disconnected the power cord, the battery held its charge. I think putting the transmission into park is the key and this is what we'll do in the future.