Learning, Wiring,

How to Wire a Bilge Pump with a Float Switch (8-Step Guide)

By the end of this guide, you’ll know how to wire a bilge pump with a float switch.

For most people, manually turning ON and OFF the bilge pump can be problematic. Especially when you are fishing, you might forget to turn on the bilge pump. The ideal solution is to wire a float switch to the bilge pump.

In general, to wire float switch to your bilge pump, follow these steps.

  • Cut off the power supply for the bilge pump.
  • Pull out the bilge pump from the bilge well area.
  • Clean the bilge well.
  • Mount the float switch on the well.
  • Complete the wiring process according to the wiring diagram.
  • Connect the bilge pump to the base.
  • Raise the wire connections above the predicted water level.
  • Test the bilge pump.

You’ll find more details below.

Before We Start

Some might be familiar with the concept of adding a pump float switch. But for some, this process can be uncharted waters. So, before starting the 8-step guide, go through the following sections.

Why Should I Add a Float Switch?

adding switch float
Video | Wu Salina

We use bilge pumps to remove the water that accumulates inside the bilge wells.

The pump connects to the battery and the manual switch. When you detect a considerable amount of water, you can turn ON the switch to start pumping the water out. It seems like a flawless system, right?

Unfortunately, not so much. The above process is completed manually (except for the pumping water part). First, you’ll have to check the water level. Then, according to the water level, you’ll have to turn ON the switch.

There are two things that can go wrong.

  • You might forget to check the water level.
  • After inspecting the water level, you might forget to turn ON the switch.

How Does a Float Switch Work?

float switch
Video | garymalm

A float switch is a level sensor.

It can detect the water level with high accuracy. When the water touches the sensor, the float switch will start the bilge pump automatically. So, you don’t need to check the water level or manually control the system.

8-Step Guide to Wire Bilge Pump with Float Switch

This guide includes the processes of installing and wiring a float switch to a bilge pump.

The installation and wiring are a combined process. So, explaining both is much better than showing you only a wiring diagram.

Things You’ll Need

  • Float switch
  • Power Drill
  • Philips screwdriver
  • Flat screwdriver
  • Wire stripper
  • Heat shrink wire connectors
  • Silicone or marine sealant
  • Heat gun
  • Ground test light
  • Liquid electric tape
  • 7.5A fuse

Step 1 – Cut Off the Power Supply

cut power supply
Video | Mark Davies

First, locate the battery and disconnect the power lines that go to the bilge pump.

This is a must-follow step and never start the wiring process with active wires. If needed, check the live wire on the pump after disconnecting the main power. Use a ground test light for this.

Be mindful of: If the bilge well contains water, pump the water out before disconnecting the power.

Step 2 – Pull Out the Bilge Pump

Snap the bilge pump from its base.

Use a screwdriver to remove the screws that hold the pump. You’ll have to disconnect the hose to pull out the pump outside. Disconnect all the wire connections.

Step 3 – Clean the Bilge Well

Inspect the bilge well and remove any dirt and leaves. In the next step, we are going to install the float switch. So, keep the inner surface of the bilge well clean.

Step 4 – Mount the Float Switch

Now it is time to install the float switch. Choose a good location for the float switch in the bilge well. When choosing a location, consider the below facts.

  • The float switch should be placed above or at the same level as the bilge pump.
  • While drilling for screw holes, you shouldn’t go all the way. Don’t damage the boat from the outside.

Finding the same level is not a difficult task. But the drilling process might confuse you. Follow these steps to avoid drilling the bottom of the hole.

  1. Find an old screw that belongs to the bilge pump.
  2. Measure the length of the screw.
  3. Transfer the length to the piece of electric tape.
  4. Wrap the measured tape piece on the drill bit.
  5. While drilling, pay attention to the mark on the drill bit.
  6. After drilling, put marine sealant on the holes.
  7. Place the screw on the hole and tighten it.
  8. Do the same for the other screw.
  9. Then, take the float switch and slide it into the screws.

Step 5 – Wiring

bilge pump wiring diagram

Before starting the wiring process, study the above wiring diagram. Whether you understand it or not, I’ll explain it step by step.

Connect the pump’s negative end (black wire) to the negative end of the power source.

Take the pump’s positive end (red wire) and separate it into two feeds. Connect one feed to the float switch and the other to the manual switch. While connecting switches, you can connect any side you desire. No need to worry about the polarity.

Then, connect the 7.5A fuse to the positive end of the power source.

Connect the other end of the fuse to the free wire ends of the float and bilge pump manual switch. After you complete the wiring, the bilge pump float switch and the manual switch should be in a parallel connection.

Be mindful of: Use Heat shrink wire connectors for all the connection points.

Why a Parallel Connection?

This is the part most people get confused about.

In truth, this is not that complicated. You can use the manual switch as a backup system when the float switch malfunctions by connecting the two switches in a parallel circuit. (1)

Be mindful of: The float switch might get broken due to electrical issues. Leaves and dirt might clog the device temporarily. When that happens, use the bilge pump manual switch.

Step 6 – Connect Bilge Pump to the Base

Now, place the bilge pump on its base. Snap the pump until it gets fixed to the pump base. If needed, tighten the screws.

Remember to connect the hose to the pump.

Step 7 – Raise the Wires

All the wire connections should be above the water level. Even though we used heat shrink wire connectors, do not take any chances. (2)

Step 8 – Test the Pump

Finally, connect the power supply line to the main power and test the bilge pump.

Take a look at some of our related articles below.

(1) backup system – https://support.lenovo.com/ph/en/solutions/ht117672-how-to-create-a-backup-system-imagerepair-boot-disk-and-recover-the-system-in-windows-7-8-10
(2) water level – https://www.britannica.com/technology/water-level

Video Reference


Wu Salina


Mark Davies

Shoreline Marine

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About Sam Orlovsky

AvatarCertifications: B.E.E.
Education: University Of Denver - Electric Engineering
Lives In: Denver Colorado

Electrical engineering is my passion, and I’ve been in the industry for over 20 years. This gives me a unique ability to give you expert home improvement and DIY recommendations. I’m not only an electrician, but I also like machinery and anything to do with carpentry. One of my career paths started as a general handyman, so I also have a lot of experience with home improvement I love to share.

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