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12v electrical system


Shawn Simmons
Started working on the 12v system. None of the exterior lights work, the vent blower motor didn't run and in general the 12v system is a bit of a mess. I pulled the old panel and am building a new one. I will post pictures later of the new panel. Biggest issue so far has been checking continuity for the various lights, etc. I have identified the positive wired for the navigation lights, the spreader lights and I have identified the negative for the blower motor.

The current major issues are.
Trouble locating the ground. it looks like all of the ground wires were connected to a single common ground that I am not certain where it terminates. I also have not found the point where all the negative wires connect. That is project #1 next weekend i work on the boat.

The wiring through the deck (mast boot) is basically shot. Insulation is gone and wires are barely together right where they go through the deck. not enough for me to splice a new wire to so I will need to run new wiring through the mast step which means I may as well replace all of the wire from the panel through the mast step and the mast.

Questions. Why am I struggling to locate ground wires?
Best way to run new wiring through the mast step.
Any good ideas that will contribute to me getting this project done correctly and efficiently.

I do have a decent background in 12v electrical systems but the 48 year old system in my boat is causing me a bit of confusion.
pictures first to last
wiring in the mast
mast step, next 2 pictures
the wiring for my anenometer
more mast step and associated wiring
Block where connections from panel to individual lights, etc
back of old panel with old switches and wiring removed.


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Loren Beach

O34 - Portland, OR
Senior Moderator
Blogs Author
May I suggest adding a negative bus bar behind the 12 volt panel? And, a separate 110 AC bus bar. Our '88 boat came with these, and I expanded them to avoid doubling up on any wires under one screw head.

There are some truly excellent threads here on owner-built new distribution panels. Some searching will be in order. And you will love the newer circuit breakers.

Also, if the spar is down where you can really work on it, this is the time to replace the wiring and the old coax.

G Kiba

Member III
I just finished re-wiring my engine control panel and now I am starting to clean up the distribution panel and AC. Not a fun job but it drives me a little crazy every time I open the panel. Not sure of the vintage of your boat but my previous 73' E27 had household wire and circuit breakers on the AC side. Your AC and DC system wiring looks fairly dated as well.

Two sources I have found to be really helpful and quick are
https:/pacergroup.net and bestboatwire.com.

Both of these sources have a good selection of marine crimp terminals, wire, and terminal blocks.

Christian Williams

E381 - Los Angeles
Senior Moderator
Blogs Author
This may be too elementary for you but it does discuss the common ground issue.



Sustaining Member
Blogs Author
Here is a discussion of running wiring through the mast step: https://ericsonyachts.org/ie/threads/mast-step-wiring-conduit-35-2.18814/#post-145229

Also, it might be time to consider ripping the entire DC system out and starting fresh. So many changes occur over the years, disconnected wires, missing grounds, etc., it's almost easier to abandon it all. When I replaced mine, I was surprised how corroded the original wiring was even in the middle of a long run. It's a big job, but you won't be left chasing voltage drops and hidden shorts.

Also, that AC outlet should be in a box! I would hate to be reaching around in there with the shorepower connected...


Sustaining Member
Blogs Author
I think the typical way is for grounds to run to a common bonding point which is a big cable that runs to the engine block (and would carry current out into the water via the prop).

To chase grounds and locate wires I have found a Klein signal trace tool helpful: