How to Wire Boat Bilge Pumps
There are several ways to wire bilge pumps, but you always want to keep due diligence in mind, especially for electrical components that could be exposed to water that makes its way into the bilge of a boat.
Whether you're using a manual bilge pump, one with a built-in float switch, or one of the new electronic sensing ones, there are certain practices and requirements that you need to meet when you're doing wiring, especially down in the bilge.
Watch the video above or read on below to learn about how we wired two types of Rule Industries (manual and automated) bilge pumps.
Tools and Parts - Bilge Pump Wiring (Rule Industries)
First, we're wiring a manually triggered bilge pump, along with a separate float switch and three-way switch, and a fuse. An in-line fuse protects the wiring in the boat if there’s a pinch in the line or something that it grounds out.
Wiring a Manual Bilge Pump
The fuse size needed for this particular application is found in our chart below, and it needs to draw somewhere in between 4.5 and 7 amps under full load, depending on the voltage as well. In our case, it requires a 10 amp fuse inside the fuse holder.
You also want to take into consideration the length of the wire that's going to head down to the combination of the pump and the float switch. If it's under 20 ft., 14 gauge wire should do it. However, if it's further than 20 ft., you may want to bring that up to a 12 gauge wire just to make sure it has enough ability to carry that additional amperage.
As for the wiring itself, resist the temptation to use just any old wiring. It’s all going to be below decks, so the wiring needs to be resistant to heat, fuel and oil, and anything else sloshing around in the bilge. Make sure you're only using US Coast Guard approved wiring for bilge pump installations.
For this particular design, a two conductor isn't going to do it. We're going to use three different conductors, because we're using a switch that can either run in automatic mode or manual mode. We’ll be using a three conductor switch and wiring.
When making these connections, twisting back the wire and wrapping electrical tape around it won’t cut it. Neither will a wire nut, since it’s completely open and can gather water and corrode. For this type of wiring, we need heat shrink butt connectors. That way when you apply heat to the surface, it shrinks down and makes a bond with the existing insulation on the wire, creating an airtight seal.
Starting with the connections at the battery, put a slight cut into the insulation on both sides of the cable, not too deep, just enough for it to split it open without leaving any rough edges.
Cut the insulation and the batting out of the way, then use a piece of heat shrink to get a tight seal at the ends of the cable.
Next up for the fuse-to-battery connections, pull the fuse out of the holder to protect it, then use a crimp type connector with the heat shrink.
NOTE: When you heat these connections up, be careful not to burn your fingers.
When it comes to the switch, you can use a regular three-way switch where it's on in one position, off in another, and on momentary hold when connected. Or you can use a simple on and off two-way switch.
With a two-way switch installation in manual mode, the float switch represents the other switch. So if you want to manually run your bilge pump, there’s the on/off hand switch, and the float switch that turns on the pump automatically if the water in the bilge gets too high. The float switch closes, then power flows through it and it turns on the pump.
The drawback to this setup is the float line is always live, so there's no real way to turn it off except to turn off the battery source itself. A two-way switch can leave you wondering whether you put the switch in the right position when you left your boat in the water. And if it gets stuck, the pump's going to keep running dry and burn up.
With a three-way switch, you can completely isolate the pump away from the power by putting it in the off position. You can activate it by putting it in the momentary position, and then empty the bilge. On run mode, it sends power to the float switch and turns on the pump. So with the three-way, you can completely isolate the pump if you have float switch failure, but you can only turn on the pump in run mode.
No matter which switch type you go with, don’t lose the wiring diagram, because depending on the manufacturer, the location and the function of each connection on the back of the switch itself may vary. For our setup, we’re going with a lighted three-way switch, which has an additional ground that has to be activated so that the light will turn on.
The center port of the switch is where the power from the fuse comes in, while the two other outputs are for the momentary and run modes.
When preparing a negative wire coming from the battery, in our case the manual wire is green, and our float switch wire is white.
NOTE: You can go either way with the wire colors; it's up to you which way you want to apply it.
You want to give a common point for the ground, so we combined these with a connector.
Our particular switch uses a quarter-inch spade type connector with the heat shrink already on it, ready to be crimped and heat shrunk.
We make our power connections to the hand switch, followed by the ground. The manual wire is green, the float switch wire is white, and that completes the helm wiring.
Working our way down to the pump and the float switch, we grab one side of the switch to connect with the white wire.
That pathway goes parallel with the manual wire (green). Both go under one connector, and it’s important make sure there’s enough length on these wires to bring it up out of the bilge, so as not to run the risk of the wires staying in the bilge water. It’s also important to make sure to use gel-filled heat shrink for a better seal. This goes to the positive of our pump.
Next, we get the ground going back up and heat shrink it all down, then connect our battery and put in the fuse.
With this three-way switch in the on mode position, when the float switch lifts, water comes in and the pump turns on. And of course with the off position, nothing happens when water comes in, so that’s where the momentary position is beneficial. With this particular switch, when the float switch gets activated, it knows the current is flowing and turns on the indicator.
Wiring an Automated Bilge Pump
Next up is wiring an integrated, automated bilge pump, which is basically a pump combined with a float switch in one unit. For this pump, we're wiring it through a two position lighted switch. This setup consists of a battery, hand switch, boat cabling and the pump.
We start by creating the connections that go down in the bilge. Just like the other setup, we prep the cable by stripping it back, and sealing the cable (20 feet long, max for this size) so it’s ready for connections.
We take our manual (or run in this case) and it’s going to piggy back on the fuse side, so it’s a direct line running back to the pump.
We accomplish this by putting it on the same terminal going to the switch itself. Our negative needs to be parallel into the switch because the negative needs to turn the light on. The negatives go together under one terminal, so that just comes back to the single eyelet that goes to the negative post of the battery.
That leaves us one last wire, the manual. We plug in our negative, battery source, input and our load on the switch.
Heading down to the pump, our negative (manual) goes through the switch, which in this case is the white wire. The wire going to the switch inside the pump goes all the way back, straight to the battery through the fuse for a constant connection.
In the off position, we put the fuse in. We then run it manually, flip the switch and put the pump into some water to activate the switch on the inside and see if it’s working.
The water triggers the pump and the light on the switch. When we lift the pump out of the water, it runs for several seconds before it shuts itself off, sensing there’s no more water to pump out.
If you never want to worry about making sure the switch is on so the pump will work, the automatic bilge pump is the way to go.
Computerized Bilge Pump
A computerized bilge pump wires up exactly like the automated pump, but with the build switch inside of it. The type of pump has electronic circuitry to where it turns the motor on every so often, and if the amperage is high enough (which would indicate that the pump is having to work), it continues to run until that amperage drops down. That means it's pumped all the water out and then it shuts off.
If you want to be able to sleep at night knowing the pump's not going to run continuously because the float got stuck, this type of bilge pump might be the best alternative for your boat.
