The phrase "tachometer dials" refers to the circular gauges on a vehicle's dashboard that show its engine's speed in revolutions per minute (RPM). Full definition
The white - lit speedometer and tachometer dials stand out against a green backlight. (kbb.com)
The «check engine» icon light embedded in the tachometer dial is basically the same one you see on every other average - to - exotic production car, and it resembles a carbureted V - 8, complete with the air cleaner on top. (automobilemag.com)
The tachometer dial... Show full review (cars.com)