How the Turn Signals on Your Car Work

It may seem like magic. You push a small lever up and your right turn signal begins to flash. Push it downward and suddenly you are telling the world that you are turning left. This process works by using some simple technology in a complex way.

The turn signals are made of several basic components.

Your car has huge amounts of wiring running in many directions. About 75 feet or so of wiring is needed to carry the current necessary to power the turn signal system. Attached at the corners of your car and on your dashboard are lights that flash to indicated the direction your are planning to turn.

The second component is the switch.

The turn signal switch has been a lever located on the steering column of most cars for over 50 years. Prior to the electronic signals, you had to stick your arm out of the window to tell other drivers that you were about to execute a turn. When it works right, this switch is designed to be pushed up or down by the driver. It is turned off when the steering wheel returns to the center after the turn has been completed. If the turn is too slight, like a lane change, the signal will have to be reset manually by the driver.

A specially designed flasher makes up the final piece of the system.

The flasher is the part of the turn signal system that causes it to blink on and off when the signal is activated by the driver. Without a flasher, the signal would have to be turned on and off manually by the driver for each blink of the turn signal. Each type of car has a relatively unique flasher to operate its respective turn signals.

Inside the flasher is a bi-metal strip and contact.

A bi-metal strip is a small metallic strip that has one type of metal on one side and a different type on the other side. When the strip is warmed electricity passing through it, the two types of metal heat at different rates. Heating causes the metals to expand. When one of the metals expands slightly faster than the other metal, it causes the strip to bend away from the contact and break the circuit. This makes the lights go out. As the strip cools, it returns back to its former position, touches the contact, and turns the lights back on. This action continues to repeat itself every half second or so until the signal switch turns off.

The candle power of the lights will determine the blink rate of the flasher.

Brighter bulbs tend to use more energy and cause the strip to heat more rapidly. The flasher has to be rated to handle the size of bulbs in use in the particular make and model of car. When one of the lights burns out, the flasher will blink very slowly or not at all because the strip heats too slowly or too little to function properly. If a wrong bulb is put in the system, it can cause the flasher to blink too quickly if it is a higher watt bulb than the system requires. The flasher will blink too slowly if the bulb uses fewer watts.