How To Replace A Bilge Pump Switch

Article & Photos by Mark Corke

Automatic bilge pumps turn on and off, even when you're not aboard, to keep your boat high and dry. If your automatic switch is faulty here's how to change it out.

Bilge-pump switches have two jobs: turn the bilge pump on when there's water in the boat and then turn it off again once the water's been pumped out. Most automatic switches are of the float type. Water in the bilge raises the float and turns on the pump. As the level drops, the switch returns to its rest position and turns off the pump. This is all very simple, but a malfunctioning float switch could cost you dearly, and these switches are notoriously unreliable after a few years. A boat could sink if the float switch fails to detect rising water levels inside the boat. A pump that fails to turn off could cause it to overheat and burn out. And even if that doesn't happen, the running pump will eventually drain the battery.

Swapping out a bilge-pump switch is normally straightforward, but there are a few things to keep in mind. So here's how it's done. (Some bilge pumps have integral automatic switches, which are not float switches and are not covered in this article.)

Old float switch

1. Before the old float switch is removed, make certain that it really is faulty. Try turning on the manual switch on the boat's dash to find out if the pump runs. Also make sure that the battery is charged. If both these checks prove positive, lift the float switch with a finger. If the pump fails to turn on, it's safe to assume that the problem lies with the float switch or its connections.

Disconnecting the bilge pump cable

2. Shut off the power by disconnecting the bilge-pump cable from the battery or removing the inline fuse.

Removing screws from the old switch

3. Remove any screws or small nuts and bolts holding the switch in place and lift the switch clear.

Tracing cabling back from float switch

4. Trace the cables back from the float switch to where they are spliced to the cables going to the pump.

Cutting the wires above existing connections

5. Cut the wires just above the existing connections and then strip back the ends of the cables, or as may be otherwise appropriate depending on the type of splice. If the copper conductors look green and corroded, a sure indication that moisture has gotten under the insulation, you may have to trim back some more until you get back to noncorroded conductors.

Connecting new switch wires

6. Connect the new switch wires. (See step 7 in "How To Replace A Bilge Pump" for instructions.) Most likely they will be too long, so you may want to trim them, allowing room for any needed securing and/or routing, before making the connections. They should not be too tight so that the cables are under tension, nor should they be too loose so that they drape in the bilge or may become entangled in moving parts. Keep the connections above the highest projected level of bilge water you're likely to have and away from splatter from the stuffing box.

Screwing new switch in place

7. Screw the float switch back in position using new hardware. Any screws or nuts and bolts should be marine-grade stainless steel. Nothing else is acceptable. 

— Published: October/November 2017

Tech Support

Degree Of Difficulty
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Tools and Materials:

  • Screwdriver
  • Electric crimper
  • Wire stripper
  • Float switch
  • Crimp-style connectors with heat shrink


About an hour.


Approximately $50–$100, depending on switch.


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