Bilge Pump Float Switch Guide

A functioning Bilge Pump Switch is one of the essential keys to carefree boat maintenance. Here we will investigate the pros and cons of various Bilge Pump Float Switches and how to fit them to ensure your boat’s bilges are efficiently monitored.

There is an adage in boating that maintenance is proportional to the ease of access, and bilges are a prime example.

Bilges are generally unpleasant places. They typically require a lot of kneeling and contortions that human bodies were not designed to make. So let’s get to making bilge monitoring a little less painful by going through the essential elements of an efficient Bilge Pump Float switch system.

Decide on the System that Suits You

Here are some of the options:

  1. Automatic with float switch connected to a battery.
  2. Manual switch to supply power from the battery to float switch.
  3. The dual system allows manual and or automatic connection to the bilge pump.
  4. An automated system with a warning light on the dashboard and a manual shut down.
  5. The automated system is connected to your cellphone.

Let’s go through each one to see what suits you.

System 1 is the easiest to wire up. The float switch is connected directly to the battery. A fuse is fitted to the live feed for safety, and the float switch is always powered on.

Advantages of this system. The bilge pump is always on, ensuring that any water entering the bilge area will be pumped out automatically.

Disadvantages. The system has no warning function to alert you that the pump is running. In addition, if the pump is run for long periods, it may drain the battery.

System 2. Fitting a manual switch and a fuse from the battery to the float switch gives you more control over the system. You can switch the bilge pump off in situations where it is not required, which will preserve the battery power.

Disadvantages. The biggest drawback of this system is that you may forget to switch it back on again when leaving the boat. This will disable the float system, and consequently, the bilge pump will not function.

System 3. You can switch on the bilge pump independently from the float switch with this system. Float switches tend to leave a small amount of water in the bilge as they reach the end of their travel before all the water has been pumped out. With the manual switch, you can extend the pump’s operation time to rid the bilge of the remaining water.

Disadvantages. Careful management of the manual switch is required to avoid the pump cavitating and running dry. Bilge pumps are generally fitted with a run-dry protection system, but I would rather not rely on that.

System 4. Now we are heading in the direction of sound control and peace of mind. Some additional wiring is required but is well rewarded with the ability to monitor the bilges from the bridge.

Disadvantages. Sometimes bringing up new wiring from the bilge to the bridge is problematic. Also, passing through bulkheads and decks is hard work.

System 5. This system operates very much like a home security system. The intruder, in this case, is water.  The system has to be powered up to facilitate the monitoring of the bilge. Notifications are sent to your cell phone, alerting you to the bilge pump working. You will need a sim card for this as well as data.

Disadvantages. It is nice to have if you are frequently away from your boat, but it is probably the most costly to purchase and maintain.

All the above systems require some electrical wiring so let’s start with the simple wiring and build from there.

Three Elements Required: Pump, Battery, Float Switch

Bilge Pump Float Switch

We are honing in on the Bilge Pump Float switch, so I’m banking that your battery is fitted correctly and secured. Batteries are heavy, so it’s a good idea to stow them low down but not in areas where they are likely to get wet.

Similarly, your bilge pump has been seated correctly in the bilge. So the first thing we are going to check is the cable—some questions you need to answer.

  1. Is it marine-grade cable? Even if you are located on freshwater, don’t skimp on this.
  2. Is it the correct size? Remember, we are dealing with DC here.
  3. Do you have the correct size lugs for the cable and the battery terminals?
  4. Remember to use the appropriate color cable.
  5. It is always essential to fit an appropriate fuse to the positive cable.

The lugs need to be correctly seated on the cable, and it is always a good idea to put a little solder through the inspection hole of the lug to ensure a proper electrical connection. Be careful not to apply too much soldier as this could create a hard spot in the cable and result in strands breaking. Just a little drop will do.

Heat shrink is a must to ensure that moisture is kept at bay. I always use heat shrink a little bigger than required, as this provides a more solid barrier. Remember to check that the adhesive is forced out of the end of the heat shrink, as this provides proof that it has been appropriately applied.

Bilge Pump to Float Switch Connection

How to wire a bilge pump ON-OFF bilge switch New Wire Marine

We have dealt with fitting lugs to fit the battery side, and now we have to check the wiring from the pump to the float switch, and I’m afraid it is here you will have to make some decisions.

At its most simple, you will need to bring the cables up from the float switch together with the wires from the pump. A convenient spot will be required where the wires can be connected.

If you need to pass through any bulkheads, you will require appropriate watertight glands.

Here is a diagram that provides for both manual and float switch energizing of the bilge pump. If you recall, this is the system we described as System 3. From the battery, two positive lines pass through fuses, and then one line passes through a manual switch, and the other line goes through the float switch.

Engaging the manual switch will energize the pump, and the float switch will engage the pump irrespective of the position of the manual switch. Therefore, by switching on the manual switch, the pump will operate regardless of the position of the float switch and whether there is any water in the bilge or not.

When using the manual switch, great care must be taken as the bilge pump could run dry.

If you would like to switch off the supply to the bilge pump manually, you will need to introduce a three-way switch. This is the situation described in System 2 but remember the danger of forgetting to switch the system on again when leaving the boat.

The advantage of this system is that if you want to clean the bilges, you will be able to switch the bilge pump off to allow thorough cleaning. Then, once the cleaning is complete, the pump can be switched on again to empty the bilge.

Fitting the Correct Connections

Bilge Pump Installation

The float switch and the bilge pump both have watertight cabling, but we now need to deal with the other end of the cable where it fits into your switching mechanism. Again, it doesn’t matter what system you choose. The basic and essential requirements remain the same.

The lugs that are fitted to the cable must suit the terminal block of the switch you are using. This will be a pin-type lug that fits into the switch in most cases. Heat shrink around the lug connection is always a good idea to prevent corrosion of the wire.

Please do use marine-type switches. They are designed to be safe and watertight. Some controls have built-in warning lights that light up to alert you when the bilge pump is running.

Other switches are available that incorporate a sound alarm to do the same job. If you decide to fit an audio function to your bilge pump, I suggest that you include an on/off switch for the audio. It can get annoying.

The Best System for Your Boat

The best place from which to control your boat’s bilge pump is invariably from the dashboard. Here most of the controls are situated and the area where a warning light is most likely to be seen.

Be careful about incorporating the bilge pump circuit into the electrical panel. Usually, you would switch the electrical panel off when leaving the boat to save the battery from running down but doing that will also close down the bilge pump.

So you will need to bypass the off position on the control panel to allow the bilge pump always to draw power. The three-way switch system which we dealt with earlier would be your answer to this problem.

Another point to remember is that the bilge pump and the float switch will not last forever, and there will come a time when they will need replacing. So make sure that the wiring you are fitting will allow for the easy replacement of those parts.

Here Are Some Recommended Switches

Amarine Made 2-Pack of 12v 20 Amp Waterproof LED On Off Boat Marine SPST 3P Rocker Switch with Light (Blue)

For smaller boats, it is often more convenient to add a pump that incorporates a float switch in the body of the pump. The Maxzone Automatic Submersible Pump is a good example of this type of pump. it will pump just over a thousand gallons per hour.

An alternative to this pump is the Amarine 12 V automatic submersible pump which has a similar pump rate.

I found the Ogrmar float switch to be an excellent and dependable unit. It is available in 12, 24, and 32 V versions and shouldn’t cost you more than twenty dollars. It is easy to install and switches on when there is two inches of water in the bilge.

PetierWeit Heavy Duty Flow Marine Boat Bilge Pump Float is another make that has proved itself to be both reliable and easy to install. It has a neat feature that allows it to be removed from the foundation bracket for easy cleaning.


Question: Where Should the Float Switch be Fitted in the Bilge?

Answer: It is crucial to locate the float switch in a position where the arm of the switch is free to move up and down. Please pay particular attention to securing the power cable to the float switch so that it does not interfere with the travel of the float arm.
It is also critical that the float switch disconnects the pump before it is starved of water. This means that there will always be some residual water in the bilge, but your pump will not run dry.
Float switches have a finite life so consider the location of the switch carefully because the time will come when you are going to have to replace it.

Question: What is the Advantage of Buying a Bilge Pump with a Float Switch Attached?

Answer: Fitting a bilge pump with a float switch attached or fitted internally reduces the required wiring. These pumps are often referred to as ‘Automatic’ bilge pumps. They are more suited to smaller boats. The disadvantage of this type of pump is that the float switch always controls the pump and no manual override is possible.
They are ideal as ancillary pumps because they are small, lightweight, and can be used as a temporary solution without any additional wiring required.

Question: How to Check that the Float Switch is Working Correctly

Answer: It is always a good idea to check the float switch before installation. The mechanism inside a float switch is straightforward. By raising the pivoting arm to the up position to simulate the switch floating in water is very much like pressing a switch to the ‘on’ position. It is possible to hear a mechanical ‘click’ on many float switches as the circuit is completed.
Using a multimeter to check continuity will provide proof of the functionality of the switch. Attach each wire from the float switch to the terminals of the multimeter and raise the float switch. When it is in the ‘up’ position, the meter should show continuity, and by lowering the arm, the continuity should be broken.


I’ve dealt with many bilge pump float switch systems, from the most basic of float switches connected directly to a battery to those connected to the DC section of a central control panel. The guiding principle is to fit the one that works for you and keep it simple.

A control switch on the dashboard with a warning light to tell you that the bilge pump is running is a good system. Add a manual switch to activate the bilge pump without using the float switch, and you will have a  pretty foolproof system that I would recommend.

As for an audio alarm, despite its annoying feature, I think I would fit one.

With the tremendous advances in cell phone technology, the convenience of monitoring the bilge pump via your cell phone is becoming an everyday occurrence. It does add additional load to your battery, but it could be a great asset depending on your schedule of visits to your boat.

As cell phone monitoring can also incorporate a security feature, I would go for one of these systems.

Looking for more interesting readings? Check out:

Leave a Comment

Your email address will not be published. Required fields are marked *

Scroll to Top