How to install a marine battery selector switch

Written by chris stevenson
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Adding a marine battery selector switch to your boat will help guard against a dead battery. The selector switch allows the power of one battery to be used while the other battery charges and remains at full capacity. Switching from one battery to the other reduces the chance of an accidental stranding. By alternating power drain between two batteries, the total power drain is distributed so neither battery loses its charge. Battery selector switches can be purchased at most marine supply stores.

Skill level:

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Things you need

  • Pencil
  • Boat owner's repair manual
  • Battery selector switch
  • Socket set and wrenches
  • Battery cable (if applicable)
  • Wire strippers
  • Battery cable eyelets
  • Phillips screwdriver

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  1. 1

    Block the wheels on your trailered boat. Disconnect the negative battery cable on the main engine battery with a socket and wrench. Choose a location for mounting the selector switch that's close to the batteries so that excess wire will not be necessary; long wires from the dashboard location will create too much resistance over time -- keep the wiring short. Mark the outline of the mount with a pencil on the transom interior plate or on the side rail.

  2. 2

    Locate the positive (red) wire from the main engine battery that goes to the starter relay or the starter. Use a socket and wrench to disconnect the starter or relay wire. Connect the starter wire with a to the number one post on the battery selector switch, using the washer and nut provided in the kit. Tighten it with a socket and wrench.

  3. 3

    Trace the positive (red) wire of the second battery to its source, which would be the extra connection on the main battery positive cable in the case of a parallel set-up. Loosen and remove the extra wire from the positive on the main battery with a socket and wrench. Connect the end of the second battery positive wire to the number two position on the battery selector switch, then tighten the kit nut and washer with a socket.

  4. 4

    Use the wire provided in the kit to connect the number three post on the selector switch to the starter or relay. If you do not have the proper gauge wire from the kit, refer to your owner's manual for the proper gauge wire. Obtain the wire from a marine supply store if it was not included in the kit. Cut a section of the wire long enough to go from the number three selector switch post to the starter or relay. Strip both ends of the wire with wire strippers and crimp on two electrical eyelets.

  5. 5

    Connect one eyelet to the number three post and tighten the kit washer and nut with a socket. Connect the other end of the eyelet to the starter relay or starter and tighten it with a socket. Route your wires in the most convenient and safe path that will lead to the selector switch.

  6. 6

    Use the mounting screws in the kit to fasten the switch to your predetermined location on the transom or hull rail. Use a Phillips screwdriver to tighten the self-tapping screws into the selector switch mount. Reconnect the negative (black) battery cable to the main engine battery post. Test the operation of the switch when you have the boat in the water and running.

Tips and warnings

  • If you opt to secure your marine battery selector switch to the transom, you might need a drill motor and bits to complete the installation.

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