Not positive but I think my water pump won't operate when I am connected to shore power - doesn't matter whether I have the water pump switch turned on or not. Think that's because the water pump is designed to turn on only when there is a pressure differential and that doesn't happen when your connected to shore water. If so - you may have more than a switch/power issue. Fortunately water pumps are inexpensive and easy to replace.
It's possible that your monoplex water controller isn't functioning and they hot wired the water pump. When my monoplex controller went south it essentially disabled all the water pump switches - finding the controller was a real chore in my rig - replacing it was easy.
