Low Coolant Indicator (Diesel)
WARNING: This page does not describe the selected car, but rather 6 other vehicles, including the 1991 GMC Pickup, 1991 GMC Cab & Chassis, 1991 GMC C3500 HD, 1991 Chevrolet Pickup, and 1991 Chevrolet Cab & Chassis. However, it is still accessible from the selected car via links, so may be relevant.
Warning system consists of radiator mounted sensor, low coolant module and instrument cluster warning light. When coolant level is low in radiator, sensor sends high resistance feedback to low coolant module. Module then activates LOW COOLANT warning light. Light illuminates when ignition is turned on. If no problem exists, light goes out when engine starts.