Cars Simplified: Everything Automotive Explained


Resistors are electrical components that resist the flow of current through a circuit. Many electrical components are resistors, and some even change their resistance level based on electrical or non-electrical factors. Because resistors can be used to reduce the amperage in a circuit, it can be used to protect other components in the circuit, or reduce the effect of power passing through the component in series with it. For example, a resistor in series with a light bulb reduces the amperage of the circuit, which reduces how quickly a battery powering the bulb drains, but also reduces the light output of the bulb.

Variable Resistors

Variable resistors are a category of resistor that has its resistance changed by factors such as heat, mechanical movement, or other factors that can be chosen to make a particular kind of sensor. As the resistor's value changes, a computer that can gather information based on that change.


Thermistors change their resistance as their temperature changes. There are two types of thermistors, negative temperature coefficient (NTC) thermistors, which decrease their resistance as temperature rises, and positive temperature coefficient (PTC) thermistors, which increase their resistance as temperature rises. Most thermistors in automotive applications are of the NTC variety. Common uses for these sensors are in coolant temperature sensors, air charge temperature sensors.


Potentiometers are varible resistors that are typically a resistor component that doesn't actually change, but instead has a contact that moves across the resistor material. A common use for this type of variable resistor is in throttle position sensors and fuel level sensors.


Rheostats are potentiometers that have two terminal connections.

Daytime Running Light Resistors

Daytime running light resistors are a type of resistor that is used to have either a low beam or high beam headlight bulb illuminate at a reduced brightness. This allows manufacturers to use a bulb that is already on the vehicle instead of adding another light source just to function as a daytime running light. This reduces some wiring, makes it more likely that failed DRL bulbs are noticed and replaced, and in many cases, reduces costs to both the manufacturer and vehicle owner.