Most bilge-pump installations are challenged on three fronts: wiring, plumbing, and capacity. In the first instance, the wires leading to electric pumps should be large enough so the voltage drop between battery and pump is no more than 3 percent. This means that if the batteries are fully charged, at 12.6 volts, the voltage available to the pump will be at least 12.2 volts. In practice, a 1,000-gph pump that draws 5 amps and is located 25 feet from the battery requires Number 10 duplex wiring. In my experience, the wiring used for most bilge pumps is undersized. The power supply for bilge pumps should, by the way, be independent of the battery switch so power is always available, regardless of its position.