Why Do Bilge Pumps Have 3 Wires?(Solved)

Why Do Bilge Pumps Have 3 Wires?

Note: As an amazon associate I may earn a small commission from qualifying purchases if you click to amazon from my site and choose to make a purchase.You can read my complete affiliate disclosure for more details

Why Do Bilge Pumps Have 3 Wires?

A bilge pump is an underwater pump designed to remove water from a vessel with a hole or damaged compartment.

This device consists of an impeller and a motor to force fluid in one direction through the pump.

Additionally, the water removal function includes the reduction of pressure as much as possible without causing damage or cavitation.

Bilge pumps have three wires for power,control and one for neutral, Connect the neutral wire to the earth, where the electrical current is coming from the earth and traverses through another wire (e.g., Control or Neutral). A pump with a neutral wire has a smoother running and ensures the motor is not heating up too much.

The following reasons explain why the bilge pump has 3 wires.


The most important function of a bilge pump is to circulate water for the boat’s water systems so that sewage doesn’t collect and become stagnant.

Because of this, the pump needs the power to operate and circulate water wherever needed within your boat. You need a pump if you have a bathroom in your boat.

The bathroom can be where people reside or just a storage area for items like toiletries and towels.


We know this is only one of the important wires here, but it helps the pump work better. A pump with a neutral wire has a smoother running and ensures the motor is not heating up too much.

If the pump has a neutral wire, it will have a better performance and running time.


To control the pump, we need to have a switch that you can connect to the pump to turn it on and off, as most of us do.

We need to have a dedicated switch or buttons to be able to turn it on and off whenever we want manually.


The most powerful wire. Most of the time, it can connect to the engine block where you can generate all electricity.

For example, a 12v battery has 12 gauge wires that provide the energy needed to work and function on our boat.

Connect the neutral wire to the earth, where the electrical current is coming from the earth that can’t traverse through another wire (e.g., Control or Neutral).


You need to ground your bilge pump just like your house in case it’s installed during a storm.

This will prevent you from getting shocked if lightning strikes your boat or the pump starts malfunctioning.

Well, it’s good that you already know these things, but when you plan to change your bilge pump, it’s best to check on these aspects beforehand.

How Can You Tell If a Marine Fuse Is Blown?

Discolored AppearanceColor that doesn’t match the pattern or is faded would be a sign.
Poor PerformanceIf the device has been used infrequently and the fuse blows when you apply 120v, this indicates a blown fuse.
 Excessive HeatIf you can feel excessive heat when touching the area where the fuse goes in or even see excessive heat rising from there, this could indicate a blown fuse, as it may have begun to overheat.
Dusty AppearanceA fuse will look dusty if used for a long time and vibrate during use. If the fuse’s box has the appearance of being dusty, this could signify that the fuse is damaged or overused.
Short CircuitIf you can see sparks or hear a sound of a short circuit happening when the fuse blows up, this might signify an excessive electric current leakage in your electrical circuits.

It could also be an indicator of a damaged fuse.
Burn MarksA burnt fuse would mean it has been used for a long time and vibrated, causing the wire to burn out. This can also serve as an indicator of your electrical circuits being overloaded.
Out-gassing Or Gas LeakageSome material found in the making of fuses, like black powder, can cause gas leakage when heated up under certain circumstances. It could be an indicator that the fuse is damaged to some extent.

How Do I Know If My Float Switch Is Working?

To know if your float switch is working, there are a few things to do:

Measure the water flow -To check how much water passes through your float switch:

  • Take a bucket or spout container and stand it near your faucet.
  • Turn the water on, and place a white paper towel or absorbent material under your faucet.
  • Plug your garden hose into your drain, and turn it on.
  • Check the flow rate of the water coming out of the spout.
  • Write down the flow rate, then check it in about one minute. It should be about the same.

Now, open a faucet or a hose bib (outside shut-off valve), and measure the flow rate again. You’re good to go if this number is less than what you got with just your faucet on. 

Meter For Current and Voltage

You can use a voltmeter or a multimeter with a built-in voltmeter and measure the amount of electricity passing through your float switch.

When your water is up, you have power if there is a normal voltage – 120 volts-. If the power goes down to zero when your water is up, your float switch has malfunctioned.

If you have the older type float switch, the good news is that the meter needs to be capable of measuring 48 volts. The bad news is that they don’t always measure “48 volts”.

But it’s easy enough to check it by doing a simple series of tests.

It would help if you had a way of testing your water pressure so that you know exactly how much water is going through your faucet.

Look At the Solenoid Coils

The solenoids are the metal coils that control the water flow up and down. You can use a screwdriver to turn the screws on each solenoid to check if they are working correctly.

If they are not functioning correctly, you should replace them. You can remove the cover from the bottom of your float switch, then gently loosen their connecting wires.

Check Resistors and Capacitors in The Circuit

You can use a volt/ohm meter or some other multimeter and measure the voltage drop across resistors and capacitors in your circuit, as well as ground loss (the amount of electricity that disappears when you touch down a circuit).

If a resistor or capacitor is too high or the ground loss is too much, your water system’s electricity may leak.

The water flow from your garden hose should be about the same as your domestic faucet. If it goes faster with just your garden hose, then there may be a problem with your spigot or faucet.

If it’s slower, there’s probably a problem with the float switch, solenoids, and water supply line.

Is There a Fuse for A Bilge Pump?

Yes, There is a fuse for the bilge pump. Typically, you can find it in the engine compartment or near the fuel pumps. You often find It near the battery. You can also locate them on or near a control panel.

They label most fuses with a number and letter combination that identifies the fuse’s circuit breaker module that it protects.

The function of the fuse is to prevent the circuit from overloading by over-currents. It does that by interrupting the current flow to the circuit breaker module.

If the fuse is blown, the circuit breaker module cannot handle excess current flowing through the circuit.

Why Do Bilge Pumps Have 3 Wires?

A fuse will burn out or have its contacts melt when you expose it to too much heat. In this case, you could not use it again.

When a fuse blows inside the bilge or fails to perform properly, there may be little to do but install a new fuse.

If you locate the fuse within an engine compartment or near the fuel pump, repositioning the fuse may only be practical with serious modification of the engine compartment.

In these cases, replacing the fuse with a larger one is possible.

If you notice that your bilge pump is not operating properly and have replaced it, you can check for blown fuses with a DMM.

If you do this, then make sure that you test the circuit breaker module. You should test the fuse for continuity between its terminals with the circuit breaker module removed.

How to Test Bilge Pump

To test a bilge pump, you should do the following:

  1. Lower the water level for a below-deck bilge pump until it’s 12 inches from the top of the inlet.
  2. Close the intake valve to cut off the water being sucked into the pump and allow pressure to build up inside it.
  3. Open the outlet valve. If you hear the pump start to run and water is thrown out of the discharge pipe, the air is in the pipes.
  4. If water spurts out under pressure without the pump running, it’s working right.
  5. It may need repair or replacement if you don’t hear the pump or see any sign of water moving.
  6. If water spurts out and the pump runs, there’s probably something blocking the inlet valve.
  7. When you open the output valve, a small amount of water may flow out. If it’s a frequent problem, try installing an external discharge fitting under the deck.
  8. If water doesn’t flow from either hose or pipe, there’s probably an air or debris blockage, or you’ve blocked one of the inlet pipes between the bilge pump and its tanks with something that won’t pull air through.
  9. If you need help finding your pump, check the pipe from the water tank to the pump with a hose clamp.

What Amount Of Water In The Bilge Is Normal?

1/2″ depth or less is normal.If you’ve looked down the side of your boat’s hull, you know there’s not much to be seen. But if you see water in the bilge, it’s time for an emergency measure.

Here is how to fix a wet bilge and prevent water from filling up again.

A wet bilge can be the result of many causes. These include:

• Poor-fitting or loose hull-to-deck joint,

• Leaking hull-to-deck joint,

• Leaking portlights, deck hatches, and companionway stairs,

• Leaking hull seams and the rudder shaft seal,

• Leaking through the galley exhaust fan ductwork if the duct is not properly installed, if the exhaust fan is not working properly, or if the connections are loose or corroded.

Water levelDepth

What Size Do I Need to Run A Bilge Pump On A Solar Panel?

A common question we get is, what size do I need to run a bilge pump on a solar panel?

The answer is 60W, and over 24 hours is 1440 Wh per day. So, if you want to maintain a battery bank at 12 volts, you must use your solar panels at 120 Watts per 24 hours.

To determine the size of your solar panels, divide 120 by the number of amps your battery charger produces to maintain 12 volts.

For example: If your battery charger takes 20 Amps to maintain 12 volts and you want to charge your batteries at 8 am and 8 pm, then 120 / 20 = 6. You would need six panels for all your charging needs to be met.


Is It Necessary To Prime A Bilge Pump?

Yes, Priming a bilge pump lets the water flow through the pump and get it started. If you’ve ever taken out the pump and sat there, you know water doesn’t just appear from nowhere.

It takes time for the pump to come up to speed. The water inside the pump bowl must flow through passages to get out of the pump.

Priming a bilge pump lets the water flow through these passages and get it started. Priming a bilge pump is practically shrugging off the “empty” label on your tank before you go for a swim and fill your boat with gas.

Depending on the type of bilge system, you can do priming through gravity or by using air pressure. If you’ve a gravity system, open the valve to your bilge pump.

If you’ve got an electric bilge pump, turn it on and let it run for 20 minutes.

Always ensure a good connection between your pump and the bilge system pipe before priming. do it right first, or pay the price with a flooded boat.

The best way to prime a bilge pump is to pour warm (not boiling) water into the inlet while running until no more air bubbles are released and your bucket’s full.

If you’ve some leftover water, stop there and close the valve. If you’ve still got a few bubbles, hook your bucket to a hose and turn the pump off.

Connect the hose to your pump and run this water through the system while your pump is running.

For gravity bilge systems, use 10% ethanol or kerosene as a priming agent. when pumping air bilge systems, use 20% ethanol or kerosene as a priming agent.

To Test A Lever Bilge Pump

The first step in testing a pump is to determine its type of pump by looking at its nameplate. It should have a description that identifies its function.

Another way to determine what pump it is, look at the lever that controls water out of the pump. If it has a lever on it, it is generally an emergency bilge pump. If not, then it is likely a manual bilge pump.

Next, you will need to connect the discharge side of the pump to something that will hold water and ensure you do not allow any air into the system. Then connect the inlet side to a hose connected to the engine.

If the pump is working, it will be able to draw water from your tank and push it through your hose into the engine, allowing you to hear the water being pushed through your pump and out of a faucet and into a sink, pot, or another container.

If the pump is not working, there is a problem with the hose, pump, or engine. If you are running a bilge alarm, it will detect the water and alarm when it is full.

Then you can check your water level by using this method before emptying your bilge.

Once you determine that your pump is working properly and connected correctly, you can empty smaller amounts of water from your boat if necessary.

To Test an Electric Bilge Pump

To Test an electric bilge pump, follow the following steps:

  1. Remove the plug from your bilge pump.
  2. Open an electric panel outlet near the bilge pump.
  3. Insert 120 volts AC into the outlet and start the pump to verify it works by watching for a water spray.
  4. Shut down power to your boat, then disconnect it from shore power before plugging it back in.
  5. Verify that the pump is still operational by starting it again. If it needs to be fixed, troubleshoot the source of power.
  6. If you’re in a marina and want to check an outside outlet for voltage, plug the bilge pump into an outlet above the water level.
  7. If your pump loses its prime the following day, empty your bilge, open all hatches, and use 2 buckets to remove water from your boat.
  8. Open the engine room and verify that you plug the pump into an outlet with power. If power is not reaching the outlet, check all connections between your bilge pump and the circuit breaker. It would help if you connected all plugs securely.
  9. If you have a bilge pump alarm, test that it works with your bilge pump by turning off its breaker.
  10. Watch for spray as you start your bilge pump to verify that it works correctly.


When buying a bilge pump, look for a long and reputable name; no matter what kind of bilge pump you have, remember that it is only as good as its service after the warranty is over.

You can repair any cheaper pumps, but some higher-end pumps are not repairable, so choose wisely when it comes to your pump.

The more expensive pumps have better-quality seals, more power, and more efficiency.


Hi! I' am Tom. I was a manager in one of the biggest stores for over 10 Years, am also an SEO by night. I don't like to call myself a blogger; they are very analytical, do email marketing, and know all SEO stuff. I faced many questions from customers about different products, and there was hardly any help on the internet. After learning all the things about these products as a manager the hard way, I decided to start a blog and help other people.

Recent Posts