• Tech Guide: Wiring Your Boat The Right Way

    A Complete Guide to Marine Wiring

    This article was originally published on Scream And Fly back in 2004 on our old website. Like most tech-related articles, they don't lose their relevance over time, and I think that is especially true of this one. I cannot overstate the importance of proper wiring, both for performance, as well as safety.

    The electrical system of your boat is its lifeline. Every system on the boat depends on it, including the engine, yet it is often neglected or its importance is underestimated. You need reliable gauges and wiring to monitor engine operating status and other vital information. Since your wiring is the only link between your gauges and engine, faulty wiring could cost you a lot more than just an afternoon and a spool of wiring. We enlisted the help of Marine 2000 located in Long Island, New York to assist us in illustrating proper marine wiring techniques.

    Your boat's electrical system is responsible for monitoring engine function, delivering proper signals and inputs to the engine, and powering onboard accessories. Although average marine electrical systems tend to be much less complex than automotive systems, they must endure significantly more harsh environments.

    When beginning your project, make sure you have wiring, crimp terminals, and all tools within reach. You're much less likely to use shortcuts in your work if you don't have to climb out of the boat for tools or materials.
    Moisture, corrosion, extreme vibrations, and temperature extremes are the norm for the electrical system of your boat. For this reason, there are specific products and rigging techniques that should be used to allow your boat's electrical system to remain reliable and safe for many years. If you just purchased a used boat, it might be a good idea to thoroughly inspect its wiring. A complete wiring project can be accomplished in one weekend on most boats, and the materials are not expensive. The following article will outline common techniques and materials that are used to properly wire a boat.

    This kind of wiring is a problem (or disaster) waiting to happen. Incorrect color coding will also make troubleshooting issues much more difficult.
    For marine use, wiring a boat with common copper wire is an often-overlooked mistake, and should be avoided. Copper wire strands oxidize very quickly, and the common byproduct of that oxidation is a green layer of oxidized metal, which will eventually degrade the conductive connection to a terminal, and ultimately fail. Always use a marine-grade tinned wire. The use of tin in the wire strands prevents corrosion, while increasing conductivity. Never use single-strand or "solid core" wiring. Vibrations will cause the wire to break inside the insulation, creating all kinds of intermittent electrical problems. I once had to troubleshoot the electrical system in a boat that seemed to have endless problems. Once under the dash, I saw the problem immediately - somebody used standard telephone wire to wire the boat! Most older telephone wire is solid-core, multi-strand, where the individual strands are insulated. As a result, the wiring developed cracks inside the insulation, and the entire boat needed to be rewired.

    Use the proper terminal for the job and avoid cheap, non-marine terminals that could corrode and fail.
    Plastic-jacketed crimp terminals should work fine for most purposes, however, we recommend the use of high quality "bare" crimp terminals, and adhesive lined heat shrink tubing is highly recommended. The heat shrink tubing slides over the base of the crimp terminal and wire, shrinking when heat is applied from a small butane torch. The shrink wrap is lined with heat-activated adhesive, and will seal the wire insulation to the crimped on terminal, providing more water resistance as well as strength to the terminal. While most shops and riggers use common plastic-insulated crimp terminals, the outer plastic shell provides very little protection against corrosion.

    Using adhesive shrink-wrap tubing will make your connections far stronger and less prone to corrosion and breakage. A small butane torch is used to apply heat.

    Terminal Crimping The Right Way

    Often overlooked is the process of actually crimping on the terminal to the wire. Bob Garone of Marine 2000 located in Deer Park, New York demonstrated the proper technique for crimping connectors. Remember to only strip off the amount of insulation required to fit the terminal on to the wire – no more. Many times I've seen riggers use simple pliers to flatten the terminal for a crimp – that is not the correct procedure. You must use a crimp tool that will dimple the terminal for an absolutely positive connection to the wire. These tools are very inexpensive, and are available at any marine or hardware store.

    Finally, never crimp the terminal from the seam; that could push apart the terminal, compromising your connection to the wire. After your crimp, slide the shrink wrap tube over the connection, and use quick, light passes with the butane torch to shrink the adhesive tube. It should only take a few seconds to shrink the tube, so be careful. If this is your first time using a crimp tool or butane torch for shrink wrap tubing, make a few practice crimps first. Always use the correct size ring terminal for the connection posts on your gauges.

    There we go - doesn't that look good? It will also be trouble-free and last for many years.
    From here, let's move on to proper gauge wiring. For most instrument wiring, use a high quality 16 gauge marine-grade wire. A good rule is to run one ignition-switched (purple) hot wire for each series of gauges per engine. For example, if you're rigging a dual-engine boat with two sets of gauges, run one switched hot source for each set of gauges. For fuel pumps, 14 gauge wire is recommended, which should run to a solenoid prior to entering the fuel pump. Do not run any other component off the fuel pump hot wire. For basic stereo applications, 14 gauge wire is recommended. If you're using custom audio system amplifiers, you should contact the manufacturer of the amplifier to select the proper gauge wiring, since this will depend greatly on the power of the amplifier.

    Standard Marine Wire Color Code Table


    Red Constant Hot
    Black Ground
    Purple Key-On Power
    Yellow/Red Neutral Safety
    Tan Water Temperature
    Dark Blue Gauge Lighting
    Pink Fuel Sender
    Gray Tachometer
    Light Blue Oil Pressure
    Brown/White Trim Indicator
    Brown Bilge Pump
    Green/White Trim Down
    Blue/White Trim Up
    Green/Orange Independant Tilt Down
    Blue/Orange Independant Tilt Up
    Yellow/Black Choke Circuit
    Yellow/Red Starting Circuit
    Black/Yellow Ignition Cut-Off


    Your wiring will start at the battery, and you'll work your way forward to your gauges and accessories. Start by running properly crimped and sealed battery leads to two distribution blocks – one for positive, and one for negative leads. The distribution blocks allow you to easily and safely tap into the battery for a direct source of power for switched and non-switched applications. Choose a mounting location that will protect the distribution block from moisture. From the distribution blocks, you can run non-switched power to the fuse block, which should be located up front, under the dash section. It is important to fuse all power conduits for safety and to prevent serious equipment damage in the event of a short circuit or circuit overload. If you are unsure about which fuse to use for each circuit, contact the manufacturer of the components being powered.

    Start your project by laying down your basic wire pathways first and loosely organizing and securing your wiring.
    This leads us into another important aspect of rigging your boat – proper supporting of wires and cables. Wires are not self-supporting structures, and you should plan your rigging so that wiring will not be subject to unnecessary movement and stress. Over time, small movements in the wiring will cause connections to break, so never use more wire than is necessary to make your connections. You can use cable ties that secure to bulkheads with screws, or adhesive anchors that cable ties can attach to. Another way to support your wiring is by the use of plastic electrical raceways, which are flexible plastic conduits that can be run throughout the boat. These conduits encase all wiring in a semi-rigid track, preventing excessive vibration and superficial water intrusion. They are also highly durable, and suited well to offshore applications.


    Whenever possible, use a nut to space stacked terminals on a single connection post. Lock washers are also a good idea to prevent loosening. This rigging will be subjected to a lot of vibrations in use.
    Run your wires so that they will not be subject to excessive heat, moisture, or any possible abrasion that can damage insulation. While you are running your wires, it is best to secure them loosely until the entire job is finished in case you need to run additional wires or relocate gauges.


    Neat, secure, and properly color-coded - this rigging will be very easy to work with for any future gauge changes or electrical additions.
    If you're one of the lucky people who have gauges mounted to an aluminum panel, it might be much easier to pre-wire the gauges to each other with the panel removed from the boat. If your gauges are installed right into the fiberglass dash unit, make sure you properly support yourself so you’ll be comfortable during the wiring. If you're comfortable, you'll be a lot less likely to rush the job or cut corners.

    Wire your gauge sets in series, connecting each like-terminal in a chain. Never stack ring terminals together – always position a nut between ring terminals on posts that require more than one terminal. Not only does this make for a much cleaner installation, but it also allows you to properly position the wiring according to your rigging. Run only enough wire that is necessary to connect each gauge to each other, and route all wires so they are easy to access and identify. To prevent the potential for loose connections, use lock washers at every terminal as well. Secure anchor points every several inches and mount cable ties loosely to them so you can route your wiring as the job progresses. Finally, as a measure of extra durability, in some cases you can loop your wiring into one coil before terminating to the gauge.


    Terminal distribution blocks allow very easy access to battery power for accessories. From here, wiring will enter fuse blocks up front.
    Periodically inspect your boat's electrical system and wiring for loose or corroded connections. The electrical system of your boat plays a very important role in safety and your boat's reliability.
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    1. Mrzip's Avatar
      Mrzip -
      EveryOne Should Read This
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