How Turn Signals Work

Turn signals were developed over a hundred years ago to solve a serious problem: to indicate what direction a motor vehicle is intending to travel. To state the obvious, when other drivers knew what direction a nearby vehicle was going, it made it easier to avoid driving into it. This was advantageous.

Today turn signals they are more relevant than ever. “Using your blinkers” is one of the most important actions you can take as a driver. Yet, some people don’t use then consistently. Too bad, failing to signal is the root cause of quite a few accidents and is probably a significant source of road rage as well.  In case you are interested, there is some interesting technology behind these critical safety devices. Thanks to our friends at Lee Dodge of Wilson, a local Chrysler, Dodge, Ram, Jeep dealer in Wilson, NC, we have the whole scoop. Let’s take a look:

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The Wiring

A turn-signal circuit gets power from the battery when the ignition key is on. The power goes through the fuse panel to a thermal flasher and then on to the turn signal lever, which is really just a fancy switch. Depending on the position of the turn-signal lever, the power either stops in the switch or gets sent to the left or right turn-signal lights. When the turn signal stalk is thrown to the left or right, the circuit is completed through the filament of the light bulb and then goes to ground. The result is the turn signal illuminates and starts blinking.

The thermal flasher

Thermal flashers are what make turn signals blink. They are small, cylindrical devices that are often located in the fuse panel under the hood or under the dashboard of your car. Here’s how it works: When you push the turn-signal stalk down, the thermal flasher connects to the turn-signal bulbs. This completes the circuit, allowing current to flow through a special strip of steel that moves as it heats up. After a second or two, a strip of steel breaks the circuit and stops the flow of electricity. It then cools down and the cycle restarts. This results in a blinking turn signal.

Self-canceling signals

Most cars have a mechanism that shuts off the turn signal when you are finished making a turn.  This makes sure that the driver doesn’t “leave the blinker on.” The way it works is this: when you turn and put on your turn signal, the turn signal starts to blink. When you steer back to straight, the turn signal cancels itself. How does it do that?

On the steering column, there is a hub with four notches equally spaced around the hub. When you lift the turn-signal stalk to signal a right hand turn, a spring-loaded roller slips into a notch in the switch housing. At the same time, a plastic lever thrusts out into the path of the hub. This forces the spring-loaded roller out of its notch in the switch housing, so the stalk springs back to its centered position.

Turn Signals in Mirrors

In the last decade, many car makers have installed turn signals in their side mirrors. This is a excellent spot for the turn signal because they are an addition indication of turning and the driver can see them without looking at the dash. Often, the mirrors contain high-intensity LEDs arranged to form an arrow that can point either left or right.

LED turning signals

The car manufacturers are slowly converting the turn signal indicators from incandescent bulbs to LEDs. This is has several advantages. First, LEDs can last 10-100 times as long as incandescent bulbs do. Plus, they are faster. LEDs light up about a fifth of a second quicker than incandescents do. That may not sound like much, but at 65 miles per hour, your car covers 19 feet in a fifth of a second. LEDs could give someone just a little more time to react when you turn signals come on.

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