How to Test a Bilge Pump

No matter what boat you're on, the bilge pump is likely going to be in the lowest, nastiest part of the boat because its job is to pump out the most amount of water that comes aboard.

Obviously you want the bilge pump, its float switch and all of its electrical components and connections to function, as they all work together to remove nuisance water and help keep the boat afloat. Watch the video above or read on below for several ways to test bilge pumps.

Boat bilge pump location

NOTE: The easiest way to test bilge pumps is to remove them from the boat. Also, bilge pump systems vary, so some of the details below may not apply to all bilge pumps. 

Tools Needed - Bilge Pump Testing


Buy a bilge pump

Pro Mariner digital multimeter


The first set of testing involves a battery, a three-way switch, an external float switch, and the bilge pump itself, with the pump and the float switch connected to the three-way switch, which is connected to a battery. With this configuration, you lift up on the float switch and it activates when the three-way switch is in the run position. When the three-way switch is in the middle position, lifting the float switch doesn’t do anything, but in the momentary position you can manually activate it.

How to test a bilge pump

Testing a Standard Bilge Pump

Step 1. Check for battery power, and make sure the fuse is of the correct ampacity and that it’s not blown. Use a test light on the load side of the fuse to see if it lights up. Next, check the battery side of the fuse, which goes through the filament and then out to the load side. If both sides light up the test light, the fuse is good.

Bilge pump testing fuse

Bilge pump troubleshooting fuse

Step 2. Put a test light to each of the terminals of the three-way switch to see if they work. Test the input, the momentary output and the on position output next to it by pushing the button for each one with the test light attached. If all three activate the test light individually, the three-way switch is working. 

Bilge pump testing switch

Bilge pump troubleshooting switch testing

Step 3. Remove the fuse so you can test the resistance values going back and through both the bilge pump and the switch itself. 

Step 4. Check to see if the wiring is complete and available to send power through the bilge pump by using the leads of a multimeter (set to resistance testing) between the black and green wires on the three-way switch (disconnected). The resistance reading should be under 1 ohm. 

Bilge pump testing wiring

Bilge pump troubleshooting wiring

NOTE: The resistance should be under 1 ohm, since the flat resistance of the three-way switch is 0.2. The flat resistance is found by putting the negative and positive leads of the multimeter together, so the 0.5 ohms is within range.

Bilge pump resistance testing

Step 5. Set the multimeter to sound verification (audio test) to check the continuity with the float switch is working by putting the leads of the multimeter between the white and green wires on the three-way switch. Lift the float switch up and listen for a beep, which means it’s working. 

Bilge pump testing float switch

NOTE: We worked with a completely sealed wiring system, where everything is heat shrunk and watertight. When testing the wires, be careful poking into them while testing to avoid making holes that would allow water to destroy the wiring. 

The next testing phase involves an automatic bilge pump with an internal float switch and a regular on/off two-way switch attached to a battery. This type of bilge pump system is hardwired going through the switch back to the pump to where you can’t shut it off, which is great for people who forget to run their bilge pumps. 

Automatic bilge pump testing

Automatic Bilge Pump Test

Step 1. Make sure that the fuse is of the correct ampacity, and use the test light on the load side of the fuse to check if it lights up.

Automatic bilge pump testing fuse

Step 2. Test that the two-way switch is working by turning on manual mode and touching the manual side with the test light to make sure power is coming in. The test light will illuminate and the pump will turn on if it’s working. 

Automatic bilge pump testing switch

Step 3. Check the wires for the motor by first removing the fuse, then measuring from the negative side back to the manual side of the motor itself on the two-way switch. In this case it’s the white wire to the negative. The multimeter should read less than 1 ohm to indicate it’s working.

Automatic bilge pump testing multimeter

NOTE: We got a 0.5. reading, which means the motor is working. 

Step 4. Test the internal switch by first reinstalling the fuse, then turning the two-way switch on manually and listening for the pump’s motor to run. Next, turn off the two-way switch and check for a test dot on the back of the bilge pump. Put your finger on the test dot and hold it for five seconds, and listen for the motor to run. 

Automatic bilge pump internal switch test

NOTE: This testing feature on the Rule-Mate pump we tested may not be available on all automatic bilge pumps. 

Step 5. Run an internal float switch test by filling a bucket or other container with water and submerging the bilge pump in it. Wait at least two seconds for the bilge pump to activate, and then another 4 seconds for the pump to start pumping out water. 

Automatic bilge pump bucket test

Automatic bilge pump float switch test

If the bilge pump doesn’t immediately start pumping out water after being submerged for a few seconds, the internal float switch is damaged and needs to be replaced.




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