K 2500 Truck 4WD V6-262 4.3L VIN Z (1992)
Shift Indicator: Description and Operation
With Manual Transmission, the SHIFT Indicator illuminates when the vehicle should be shifted to the next higher gear for better fuel economy.
Battery voltage is applied to one side of the bulb. The other side of the bulb is switched to ground by the ECM which uses engine data such as rpm,
vehicle speed and intake manifold vacuum to compute an efficient shift point.
