Join Date: Apr 2006
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In theory you could. In practice, you would be creating a path between two different "12" volt sources, one being perhaps a real 12V at the idiot connection, the other being 12-14.4V at the battery positive. that can set up a voltage loop which wastes power and screws up other things, like the brains in the regulator. Whether it works well or not will depend on the details of your setup.
So, you could try setting it up that way, and using a voltmeter and ammeter to check and see if it is behaving nicely. Or, use the idiot connection to power a relay. Idiot on, relay on, and if you use a "double throw" relay there will be a set of contacts that are OFF when the relay is on. When the relay turns off (because the alternator is off) another set of contacts comes ON, so the buzzer only comes ON when the alternator and relay are OFF.
(And of course that relay takes no power unless the alternator is ON.)
Your choice, spend $5 on a relay that isolates things and be sure are isolated, or take the multimeter to see the details. Or, just take a chance that the simple thing works. (I'm often not that lucky.[g])