A word of warning before we begin. Tech savants will love the detailed content in this 37-minute video that tells you everything you ever wanted to know about turn signals, including why they never seem to flash in sync with other cars on the road. However, for those not seeking a degree in electrical engineering, here's the takeaway. Modern electrical components with computer control are more precise, so sometimes they can match up.
That's a very basic interpretation of this clip, so here's a bit more explanation without falling down a rabbit hole. In the days before computer control, automakers used fairly straightforward electrical circuits to make turn signals work. The magic came from the Eh,turn signal relay, which wasn't actually a relay according to the video. It worked via a bimetallic strip, basically a way of converting heat into a mechanical action that functioned like a switch. With the turn signal on, the heating and cooling of the switch caused it to alternate back and forth, flashing the lights. This was also the source of the telltale clicking.
It was definitely effective, but not remotely precise. Even tiny variations in the design, materials, and power could cause the switch to activate at varying intervals. As such, this is why turn signals on different cars – even those of the same make and model – never quite matched up. And we'd bet a gazillion dollars every single car enthusiast noticed the lack of symmetry at least once while sitting at an intersection waiting to turn. Except BMW drivers, for obvious reasons.
These days, however, it's all about computer control. Those heat-activated analog switches now have small computer chips that regulate the power, and those are extremely precise. There can still be plenty of variation between makes and models, but as this video clearly demonstrates with three newer vehicles from General Motors, getting synched up in the turn lane is certainly possible. And for all the obsessive drivers out there who appreciate symmetry, that's an extraordinarily good feeling.
Expect BMW drivers, for obvious reasons.