Bronco L6-300 4.9L VIN Y 1-bbl (1983)
Temperature Warning Lamp/Indicator: Testing and Inspection
A bimetal temperature switch located in the cylinder head control the operation of a temperature indicator light with a red lens. If the engine cooling
system is not functioning properly and coolant temperature exceeds a predetermined value, the warning light will illuminate.
If the red light is not lit when the engine is being cranked, check for a burned out bulb, an open in the light circuit, or a defective ignition switch.
If the red light is lit when the engine is running, check the wiring between light and switch for a ground, defective temperature switch, or overheated
cooling system. As a test circuit to check whether the red bulb is functioning properly, a wire which is connected to the ground terminal of the ignition
switch is tapped into its circuit. When the ignition is in the ``Start'' (engine cranking) position, the ground terminal is grounded inside the switch and the
red bulb will be lit. When the engine is started and the ignition switch is in the ``On'' position, the test circuit is opened and the bulb is then controlled by
the temperature switch.