Manual bilge pumps are controlled by a separate float switch that turns the pump on and off when water levels rise and fall. Electronic automatic pumps measure current draw while the motor is spinning, and infer water levels from that. This means that the design of a typical electronic automatic pumps require it to turn on for a few seconds, every few minutes, to permit that measurement. When the pump spools up with no water load to carry, current draw is very small.

In this video, we use an oscilloscope to document current waveforms and exactly diagnose the failure mechanism of a RULE 27SA automatic bilge pump in a boat. We discuss the design considerations that make this style of pump prone to component failure, and we convert a boat with an automatic pump to a manual Rule 27DA pump controlled by a separate Rule 35A float switch.

i go on to break apart the pump and document the failed component inside. In a prior video three years ago, when an identical pump failed, I showed a similar presentation, with a different cause of failure and a different diagnostic pathway. That old video is still worth a look, to show an overall view of the system, to show how to inspect the anti-siphon valve, and to see the breadth of other diagnostic tests you may find useful. That video is here
   • Marine Bilge Pump Troubleshooting and...  .

This is an amateur presentation, offered in good faith, for free, but with no guarantees as to safety or accuracy. All DIY repairs come with risks, both to the individual, his property, and potentially risk to others. Any misadventure you encounter if you decide to accept the risk of DIY repair is on you.