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If I have a fuel, temp. or oil pressure gage with 3 posts on the back of it in my hand. Is there a way to check (multi-meter or other) the gage to determine which is positive, ground (negative)and the post for current from the sending unit (without toasting the gage)?
Thanks,
Don

there is usually no power from a sending unit, they are normally a regulated ground.

you will have 4 connections usually, look for the light, this will be one power from the light switch, it needs a ground to turn on the bulb so feed power to the light and then ground the other terminals, this will indicate which of the other three is ground.

one of the other terminals is power and the other is sensing, knowing the ground, do a continuity test from the ground terminal to the other terminals the sensing wire should be open circuit and the power should show continuity.

it will scrap the gauge if you supply power to the sensing wire.

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