by brian_bp » Sat Sep 06, 2008 4:56 pm
I agree that it seems likely that the "ground" connection is for the light.
Power would be input (from the battery or where ever), leaving ACC as the output to your 12-volt "stuff"... apparently it is labelled as an on-off switch for an automotive accessory.
To test, I would use an ohmmeter between terminals: Power to ACC should be open (infinite resistance) when the switch is off, and nearly zero resistance when the switch is on. Power to Ground should have some resistance - the resistance of the light; if it is an LED light, it may show high resistance because the tester voltage isn't above the LED threshold, but if you see high resistance there you can just hook it up to 12V (+ to Power and - to Ground) and confirm that the light goes on.
Does this switch light up only when switched on (likely, and what you want), or only when switched off (done on some switches so you can find them in the dark), or all the time (pointless here, but indicates that power is available). Lighted switches come in all of these versions.