• Here’s Why Turn Signals Never Synchronize Between Two Cars

Who knew what goes on behind the scenes when you flick that indicator stalk

There must’ve been some point in time that you would’ve tried to see if two turn indicators sync with each other or not. There are high chances that you would’ve noticed this at a traffic light. If you haven’t to date, perhaps you will after reading this article and watching the video. But, if you have noticed it, then you must have wondered why on earth don’t two indicator blinkers ever sync. It used to drive me nuts until I figured out the reason behind it. For all you folks with OCD, this will certainly calm your nerves.

There Are Far Too Many Variables To Ever Get Them To Sync

Here's Why Turn Signals Never Synchronize Between Two Cars
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Most of the indicator lights use incandescent bulbs and their blinking is controlled by a relay and a resistor/capacitor circuit which is powered by the current produced by the battery. To elaborate more on this, there is a thermal switch in the blinker relay which is essentially a small spring with wire coiled around it, and a slightly bigger, curved spring.

When you flick the indicator stalk, the current is passed to the coil wrapped around the smaller piece and it heats up and expands until it comes in contact with the bigger spring. Then the current is passed through the two springs and the coil begins to cool. This keeps on repeating and that’s how the blinker works.

Now, imagine this happening in real time. Since there are too many variables here, it is very rare for any two replays to blink at the same rate. The variables that cause it to react at different points depends on how much current is being passed to the circuit, the ambiance, and the temperature.

Thanks to all these variables, the coil heats and cools at different rates than the other vehicle’s lights. Then, of course, there’s a difference in the material used to make the circuit. Sometimes, you would’ve noticed that the blinkers of two different cars sync for a few seconds, but they soon un-sync and blink at their own rates.


Here's Why Turn Signals Never Synchronize Between Two Cars
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Due to some manufacturing tolerances as well, no two resistor/capacitor circuits are ever the same, even if they are built at the same time. But, there are some very rare cases where the blinkers fall in sync. Check out the video at 3:28 and you’ll find an example.

Sidd Dhimaan
Associate Editor and Truck Expert - sidd@topspeed.com
Sidd joined the Topspeed.com team in 2017 as an intern and in less than a year he earned a full-time position as an associate editor and junior automotive expert. He is currently our pickup truck expert and focuses his attention on heavy-duty and off-road vehicles.  Read More
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