How to Wire an Ignition Switch on a Boat

Updated February 21, 2017

Wiring the common three-post ignition switch for the outboard may be a mystery to some boaters who wonder how or if the switch is grounded and whether they drain their boat's starting battery by leaving the ignition switch in the "on" position to listen to their radio while they fish. Some boaters may understand that most of the stuff on their boat is simplicity itself, but they balk when faced with anything electrical. No need to fear; all ignition switches have the same basic function in spite of added features, and the basic circuit is the same for all.

Solder the solenoid wire to the "S" terminal on the back of the ignition switch using a soldering iron or pencil and silver core solder. Boat wiring is colour coded, and outboard manufacturers have colours in common. The wire from the starter solenoid is yellow even if it has a stripe of a different colour.

Solder the battery wire to the "B" terminal on the back of the ignition switch. This is the wire that comes from the positive side of the battery. It's the red wire. If it has a fuse on the wire it will have a stripe of a different colour.

Solder the black wire, or the wire with black on it, to the "I" terminal. This is the wire to the boat's common ground.

Once the soldered connections are complete, coat each with a spray vinyl insulation.


Your starting battery will run down if you leave your ignition switch on. If you have a house battery in addition to the starting battery, turn the battery selector switch to the deep-cycle house battery and turn the ignition switch off.


Check the wiring information in the boat owners manual for specifics about your boat's ignition switch.

Things You'll Need

  • Solder iron
  • Silver core solder
  • Spray vinyl insulation
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About the Author

Will Charpentier is a writer who specializes in boating and maritime subjects. A retired ship captain, Charpentier holds a doctorate in applied ocean science and engineering. He is also a certified marine technician and the author of a popular text on writing local history.