The first thing that will need checking is the battery. You need one for emergency braking and the converter may not work without one. The converter may be primitive by today's standards and could be hidden underneath an interior fixture or in an exterior storage space. To check converter function, measure voltage across battery terminals. It should be 13.5V or greater.
Water pump and other appliances may not work without adequate 12V power. There should be some fuses in your rig and, possibly, a circuit breaker close to the battery. It's a good idea to check all connections, including inside any junction boxes, that you don't have any corrosion issues.