12 Volt Electric Panel Main Multifunction Switch

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Veteran Member
Nov 20, 2009
United States Of America
Vessel Name
Reef Drifter
Vessel Make
1983, 34 ft., Marine Trader
Here is a look at part of the interior of the 28 year old main panel 12 volt switch that I just removed and replaced with a new switch.* I can see why it did not work so good all the time.* It appears there was some arching going on at some time in it's life.* The switch is pretty heavy duty but the years took their toll.*


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Here's a picture of our 120 VAC switch that failed last year.* We were lucky that we were on board.* Looks like the same manufacturer.


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As a general rule, it is best to switch off all individual loads before shutting off the main switch or breaker.*This minimizes or eliminates any current through the switch, and prevents arcing.*

The inverse should be followed when powering up. Turn on the main switch or breaker, and then individual loads.*
Many of the older boars do not have a breaker between the boat shore plug in and the main AC selector switch which is the main cause of electric fires.* So a double throw with polarity breakers should be installed.* Also a mentioned above turn off the high amp demands before switching the main selector switch.

Good Advice on load shedding before switching. This also applies to onboard generators - start the generator under no load conditions, and make sure loads are turned off before switching to generator power. Reverse the process for shutdown - take all loads off the generator first before shutting it down. Shutting down under load in particular can generate some nasty transients in the generator, which can lead to failure.
Great advice from all. Before I changed my 12 volt main switch last week I would get a 9 or 10 volt reading on my GPS voltage alarm and sometime the GPS would turn off for no good reason. After seeing the inside of that old switch now I know why. Now I get over 12 good steady volts all the time with the new switch in place.
"Now I get over 12 good steady volts all the time with the new switch in place."

Keep fixing , 12V is a dead battery ,

12.8v is what you need, and 14+v with the engine on is normal.
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