SJ23 Tech Tip E07, (Issued 2001-09-08) Bob Schimmel


POWER UP WITH OUTBOARD GENERATOR - Transom Electrical Connector for Starter/Generator.

For those of you who trailer your boat to/from the water regularly wouldn't it be nice to quickly connect the outboard engine to the battery in such a way that the power cable is out of the way of cockpit activities?  I mounted one on Panache by installing an external connector through the transom.  What a relief. 

There are marine connectors designed for this purpose but they are also expensive and rightly so if you review the operational requirements; water proof, electrical isolation, equipped with a weather proof cap to keep water out and a strain relief to support the cable.  All very necessary.  However, I've found the equivalent (almost) in the form of a four pin automotive trailer connector at far less cost.  The requirements under the bumper of a vehicle are not that different from the marine environment.

  • The metal case of the connector is aluminum so that solves the corrosion problem.

  • The electrical pins are made of brass and are big enough to handle the current demands of the electric starter.  The six amps of charging current from the generator is minimal in comparison.

  • The mounting flanges secure and seal it properly to the hull. 

  • The spring loaded flap includes a one tooth ratchet to lock the male and female connectors together.  Piece of mind while under way!

  • The cable entry of the connector housing (hull side) is water tight with a generous application of Sikaflex.  Similarly I sealed the male housing (engine side) with Sikaflex.  So the connector is still water tight. 

  • The connector is polarized so you always plug it in correctly. 

  • The one feature this connector lacks is a water tight cover.  I solve this with a judicial blast of OMC 6in1oil on the pins to protect them from corroding.  Have never had a problem to date. 

CONNECTOR ASSEMBLY To increase the current handling capacity of the connector I doubled up on the pins by splitting the wiring between them.  Two pins conduct the positive current and the other two pins conduct the negative.  I used oversize stranded wire, stripping the insulation back about 3/4" and forming two parallel strands to slide into the receiving holes of the pins.  Make ABSOLUTELY certain you have the same polarity on the jack (hull) and the plug (engine).  If you cross wires on any of them you will have a very dangerous electrical short to the battery.  So disconnect the cables connected to the battery and use an ohmmeter to confirm continuity.  Positive to positive and negative to negative with NO shorts between.  Finally, connect the cable to the battery and using the voltmeter read the correct polarity on the hull connector. 

The pins in the hull mount connector are set in a Bakelite barrel that is locked to the housing with a small set screw.  To water proof this I disassembled the connector and coated the Bakelite barrel with Sikaflex.  Then slid it back into the connector housing, screwed the set screw in place and let the Sikaflex cure.  This will likely be a mess to undo if maintenance is required but my solution is to buy another connector since they are relatively inexpensive. 


  1. Always support DC power cables (especially heavy ones) for their full length, cable tray, conduit, etc.  The last thing you want is a bundle of loose heavy wires swinging with the motion of the hull.  This wears the insulation away, strains the connector and ultimately invites an electrical short.  Any of these is a recipe for disaster considering that these cables are connected directly to the primary buss bars and then the battery. 

  2. It is best to mount and support the power cables high up in the hull, away from the bottom and especially away from any loose objects that could snag them.  Add a bit of pull as the object slides with the heel of the hull and you have another disaster.  So secure the wires well.

  3. Spray the connector pins annually with a light coating of OMC 6-in-1 oil, WD40 or ATF to prevent corrosion.  This is the trick that converts a connector from dry use to wet use that can operate on the water. 
  4. See Tech Tip E01 for wiring here and here.

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