A shift light in a 1991 Chevy Corvette (or any car with one) comes on to indicate the optimal RPM (revolutions per minute) to shift gears for best performance or to prevent engine damage. In a car like the C4 Corvette, the shift light is likely designed to alert the driver to upshift at or near the peak power RPM of the engine. Failing to shift at this point can lead to less efficient acceleration or, in some cases, damage to the engine.
There isn't a single universal setting for a shift light in a 1991 Corvette. It's possible the light's activation point was adjustable by the previous owner, or it might be malfunctioning and activating at an incorrect RPM.
