12 Volt Boat Electrical Systems

12 Volt Electrical Systems

By Capt. Charlie Beadon

One of the primary systems on all boats is its electrical system. Although often ignored this simple system runs all of your pumps, electronics, trim motors, and starters; so basically speaking no power equals no boating. Today were going to discuss how you can keep your 12 volt electrical system in good working order and also how to trouble shoot and fix your boat when problems arise. Remember that today were going to be talking about simple 12 volt systems and anything that goes beyond the scope of this discussion should be handled by a professional to avoid damaging your boat or personal injury.

UnknownFirst, let’s look at what 12 volt DC power is. Your house runs on AC or alternating current, where as your boat runs on DC or direct current. Direct current is very easy to work with and in most cases relatively safe especially when dealing with the small gauge wiring and low amperage on a boat. The reason that DC current is so appealing to boaters is that it is portable power…power from batteries. When dealing with DC power just think about a battery; you have a positive terminal (hot ) and a negative terminal(ground), when you complete a circuit between the positive and negative poles you will draw energy from the battery. Conversely, any break in either the positive or negative wires will stop that draw. Most electrical devices will have a positive and a negative lead, the negative wire will ground directly to the boat or battery and the positive wire will break at specific points (such as fuses and switches) to turn the device on and off.

Next, were going to discuss the various tools and hardware needed for working on your boats electrical system. In my electrical bag I keep a pair of wire cutters, wire strippers, multi-meter, light probe, heat gun, wire brush, electrical tape, T-9, various heat shrink crimp connectors, red and black marine grade wire and fuses. I keep a separate pair of wire cutters (or dikes) and wire strippers, good pairs of these tools are essential for cutting wire, stripping the casing off of wire and smashing crimps. The multi-meter is a great tool for trouble shooting. I primarily use the multi-meter to test for continuity (checking that there are no breaks in a single wire) and to test a circuit for 12 volt current between a positive and negative wire. A light probe is an easy way to test a circuit, you simply ground one end of the probe and touch a positive (or hot wire) with the other end, if you have power the probe will light up. A heat gun or a lighter is used to melt heat shrink connectors creating a waterproof seal. A wire brush is used to clean exposed wires and battery terminals. Electrical tape is used to temporarily seal connections, but should never be used as a long term sealant in place of heat shrink connectors. T-9 comes in an aerosol can and is sprayed on exposed connections and battery terminals to prevent corrosion. Crimp connectors are used to splice two wires together, or to attach a wire to a device such as your battery or a switch. Using heat shrink connectors keeps salt water away from copper in your wires which will lead to corrosion and ultimately a break in the wire. Marine grade wire comes in different sizes and colors. To choose the size (or gauge) of the wire you need to read the instruction manual for the device that you’re trying to install, and as far as color I generally use only red and black (red for positive and black for negative). Keeping a good selection of fuses and using the recommended fuse for the application is very important. Fuses are placed in line on the positive wire and are designed to melt thus breaking the circuit at specified amperages. If you use a fuse that is too small for the application you will continually blow the fuse. Conversely using fuses that are too large can result in damage to your electrical system or fire.

imagesWhether you’re at the dock or on the water being able to quickly identify a problem will save you money and aggravation. I’m going to give you a few trouble shooting tips to help you fix your boats electrical system in a pinch. If you really want to make things easy on yourself down the road I would recommend labeling all of your wires upon installation with a label maker. Let’s say for example that you go down to your boat and your GPS won’t turn on, your lights won’t work or possibly the engine won’t turn over. These are all possible scenarios that you can trouble shoot by going through the following steps. First, check the battery; ensure that the battery is charged, your battery selector switch is on, the terminals are free of corrosion and the nuts are tight. Next, check your fuses; find the fuse that corresponds to the device without power and visually inspect the fuse then check it for continuity with the multi meter. This is also a good time to ensure that the fuse fits securely into its holder. If you have a light that is not working pull the bulb and check it in the same way as a fuse. Next, check all connection points for the positive and negative wires. For example, at the battery selector switch, the fuse panel and rocker switch (sometimes these wires will become corroded or simply fall off at a connection point). Next, using a multi-meter you need to check the negative and the positive wires for continuity and voltage and then the switch for continuity. Finally, you may need to consider that there is something wrong with your using device, but before you send the device in for service or throw it away you may want to disconnect it completely from your boats electrical system and hard wire it to a charged battery to see if it works.

Finally, I want to discuss things that you can do to protect your boats electrical system. The number one enemy of a boats electrical system and electronics is saltwater. Saltwater causes the metal components of your electrical system to corrode and thus break down until they can no longer carry a current. Knowing this you should be able to protect your boats electronics by simply keeping them salt free. To start with we need to protect any break points in a wire (for example a crimp or connection point) by waterproof sealing it with a heat shrink connector. Next, keep exposed electrical connections (such as battery terminals and switches) in a dry area and coated with T-9. If you do see corrosion building up on a connection simply knock it off with a wire brush and recoat with T-9. Keeping salt from building up below decks is as important as rinsing the outside. After using the boat don’t be afraid to spray out your bilge and battery system with fresh water. Occasionally rinsing your boats engine block, drying and then coating with corrosion block can go a long way. The key to keeping your electrical system in good working order is as simple as keeping the salt out.

Captain Charlie Beadon




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