WARNING LIGHTS
The warning lights in a vehicle's instrument cluster are used to alert the operator of conditions affecting many different vehicle functions. Warning lights can be used in place of a gage, or as an enhancement to a vehicle with gages. Warning lights can be controlled directly by sensors or indirectly by the vehicle control module. One of the most common warning light systems is the sender controlled ground type of warning light. The warning light will have a twelve volt supply voltage with the sender completing the ground circuit to illuminate the light when there is a failure. This type is most commonly used for parking brake warning lights, low oil pressure lights, and engine coolant temperature lights.

Charging systems commonly use a warning light that uses a system called the balanced circuit. The warning light receive battery voltage on the input side of the light, while the ground side is connected to the alternator output circuit. When the key is on, and the engine is off, current will flow through the light and ground inside the alternator. When the engine is running, current will flow out of the alternator output circuit and will stop current flowing through the warning light by equalizing voltages on either side of the bulb.

Warning lights are used by vehicle control modules to inform operators of system failure or malfunction. One example is the Service Engine Soon light. This light is operated by the control module using a driver inside the control module. If the control module has a system failure or a system operating outside of its control parameters, it will illuminate the Service Engine Soon light. Other automotive systems will use a similar system to operate their respective lights. The anti-lock brake module may use the brake warning light and an anti-lock light to warn operators.

IGNITION SWITCH
A key operated switch that supplies current to the devices needed to start and run the vehicle. The ignition switch can also supply current to automotive accessories. It contains several set of contacts that can carry higher current loads. Some are designed to allow current to ignition and fuel components when cranking, while others are designed to limit current flow to unneeded components when cranking.