As you probably can imagine, early automobile drivers signaled to pedestrians and other drivers their intention to make a turn with their hands. They probably pointed to the direction that they were about to turn to. After a period of time, a more uniform method of communicating was likely developed, sort of like bicycles do today.
Then they went electric
There was a big problem with hand signals, however: you couldn’t see them at night. According to the December 1985 issue of Popular Mechanics, the first example of an illuminated electric turn signal can be attributed to Edgar A. Walz. In 1925, he developed and secured a patent for one and tried to market it to major car manufacturers. Believe it or not, the major car manufacturers just weren’t interested and the patent expired fourteen years later.
It was different in Europe
The automotive turn signal situation in Europe started differently. In the 1940s, the solution for signaling turns was via curious little semaphore-like indicators. They were called “Trafficators” and they were illuminated and were powered by electro magnets that swung up when they were engaged. When they were “off”, the trafficators folded back into the door pillars. Google the word “trafficator” and you will see what these looked like. They were used on Volkswagons for many years.
Then America got involved
Back in the States, Buick was the first U.S. automaker to offer factory-installed flashing turn signals. Introduced in 1939 as a safety feature, turn signals were advertised as “Flash-Way Directional Indicators” and were an option. These flashing signals only operated on the rear lights. In 1940, Buick enhanced their directional indicators by extending the signals to front lights too and adding a self-canceling mechanism. In that year, directional signals became standard on Buick, Cadillac, LaSalle, and the Hudson vehicles yet still optional on Chevrolet, Oldsmobile, and Pontiac.
The Sixties brought other innovations to turn signals. Initial plans called for Ford to install blinking sequential rear turn signals on their 1964 Thunderbird but installation was put off for more than a year while they were approved by regulators. 1968 marked another “major” change as the Federal Motor Vehicle Safety Standard 108 required amber (rather than the earlier white) lenses for front turn signals (rear signals could be red or amber.)
Today, LEDs are common
Today, the staff at Newark Automotive in Newark, DE, a full-service Chrysler, Dodge, Jeep, Ram dealer, says many new Mopar cars use reliable light-emitting diode (LED) technology for signal lighting. Such lights do not depend on lens color, the semiconductors within emit true red and amber hues. LED lights are very efficient and ultra-bright, it may not be long before filament-style bulbs will have been phased out completely.
Though the basic turn signal technology hasn’t changed in years, future improvements may include increased luminous strength and reliability. There has been some talk about intelligent turn signals that will sense when the lights should be activated.