what is a rheostat in automobiles?

Answer 1

a rheostat a variable resistor

at least in older cars,

interior light dimmer
windshield wiper delays
radio volume.
blower moter speed (ac and heater blower motor)

Answer 2

Contrary to the above answer, I don't believe there is a rheostat in automobiles. The windshield wiper delay is an RC constant which is changed when you twist the wiper control on the end of your turn signal control. When you turn the wiper speed adjustment, you're just swapping in a different value for R or C. You can use very low power components to do this. Why you would need a "high power potentiometer"(rheostat) to do this is beyond me.
A perfect example of a rheostat is the controllers for electric slot cars. When you pull the trigger, you are changing the position of the lever on the coil of wire with a DC voltage across it. When you pull the lever, you are changing the contact point from min voltage(off) to max voltage(full speed).

Answer 3

Brian L and tlbs101 are both completely correct. I wish to add that rheostats generally have a ceramic body because they are usually designed to withstand a lot of heat. A good mechanic will often use a very large rheostat to load test an automobile's battery. Such a device is, of course, test equipment and is not part of the car.

Answer 4

What answerer #1 said is true. I'll add:

A rheostat is also called a potentiometer -- but rheostats are usually rated for higher power.

Another example is in the variable windshield wiper delay. you are using a rheostat when you adjust the delay of the wipers.

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Answer 5

It's a variable resistor. One example you're probably familiar with is the interior lights - that little knob you turn on the dashboard to make them brighter or dimmer? That's a rheostat.