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Author Topic:   Ignition Key Switch Accessory Loads
pcrussell50 posted 12-26-2012 08:50 PM ET (US)   Profile for pcrussell50   Send Email to pcrussell50  
I read Jim's great article in the reference section:

I am wiring up a non-Whaler boat with that will be powered by an Evinrude motor and an Evinrude remote control and ignition switch--the same as what Jim has in his article.

I am thinking of which [electrical loads] to put on the B [that is the terminal that is connected to the Battery] and A [that is the terminal that is made live by the key switch] terminals of the ignition, [compared to] which [electrical loads] to put on a circuit that you don't shut off with the ignition key. The ones not on the key will still of course be able to be shut off with a main power shutoff like a Perko battery selector or the like. So I was thinking that basically all I want to be powered by the ignition switch will be the gauge package. The bilge pumps, SONAR, running lights, stereo, steering wheel motor tilt switch, and solenoid tank selector valve (twin gas tanks, one under each gunwale), would be on a separate power distribution.

This is a simple little 18', padded-V, fast-hull, fresh water recreational boat. Basically a bass boat hull bottom with a bowrider layout. No trim tabs, the SONAR is a Lowrance new but simple and cheap, more for curiosity than hardcore fishing, (though the hull has a spot for a thru-hull transducer, which I will use). This will be a single battery system--at first. There is room for another.

Any holes in my plan? What would you change?


jimh posted 12-26-2012 11:28 PM ET (US)     Profile for jimh  Send Email to jimh     
In most instances the electrical loads powered from the ignition key ACCESSORY circuit should be limited to devices like the engine gauges and other electrical or electronic accessories associated with the engine operation. The circuit is only able to supply a few amperes of current. Typically it is fused somewhere inconvenient to access, like under the engine cowling, and the fuse rating should be checked to see what the engine manufacturer has used to protect the circuit. It is hard to predict what the fuse rating in Amperes will be.

You certainly do not want to put any high-current load on the ignition key ACCESSORY circuit.

Also, you are making a MAJOR error in thinking that you can connect loads to the B terminal at the key switch. That is a horrible plan. You need to add your own auxiliary electrical power distribution from the battery to the helm. Any load connected to the B terminal at the key switch will be on the same fused circuit as the A terminal.

seahorse posted 12-27-2012 07:37 AM ET (US)     Profile for seahorse  Send Email to seahorse     
The factory has a MAXIMUM limit of 5 amps going through the ignition switch plus does not recommend radios or electronic accessories on the engine wiring.
pcrussell50 posted 12-27-2012 12:13 PM ET (US)     Profile for pcrussell50  Send Email to pcrussell50     
Got it guys. Thanks. The key lock switch didn't _look_ that robust anyway.


jimh posted 12-27-2012 02:01 PM ET (US)     Profile for jimh  Send Email to jimh     
The typical outboard engine ignition key switch sufficient for the loads it was designed to provide current to; it's just not designed to be the electrical center.

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