n. a light (instead of a meter) on a car's dashboard that indicates the state of various things concerning the operation of the car. (Alludes to these lights' elimination of the knowledge required to interpret a meter reading, making them suitable for idiots.) : I don't want idiot lights. I want meters!
Dictionary of American Slang and Colloquial Expressions by Richard A. Spears.Fourth Edition. Copyright 2007. Published by McGraw Hill.
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WordNet
idiot light
noun
a colored warning light on an instrument panel (as for low oil pressure)
