A variable resistor called a rheostat has two connections, and hooks up in series with a voltage source to vary its level from the full voltage to nothing. Rheostats appear in thousands or electrical and electronic applications for a multitude of uses. When you vary room lighting with an adjustable knob, you use a rheostat. Since there is no specific use, you must have electrical skills to use a rheostat not already installed in a device. You must know how to connect wiring safely, and know how to select and use all applicable tools and hardware.

Electrician
credit: Comstock/Comstock/Getty Images

Step 1

Shut off the voltage source to the device that you wish to control with a rheostat. Since rheostats come in a huge variety of sizes, this could be a tiny electronic circuit or a huge motor.

Step 2

Connect one wire of your rheostat to either one of the two leads from your voltage source.

Step 3

Connect one lead from the electrical device you want to control to the other lead of your rheostat.

Step 4

Connect the other lead of the device you want to control to the other lead of your voltage source.

Step 5

Turn the power to you voltage source back on.

Step 6

Vary or turn the rheostat until your device reaches the level at which you want it to operate, be it light intensity, audio volume, heat, the speed of a motor or any other control.