I think the electronic relays may be cheaper; and having less moving parts they are theoretically less prone to break.

So, why do cars still use mechanical relays for turning lights?

  • 2
    You also need to consider that the high wattage of an incandescent turn signal all but requires a mechanical relay. To replace just the mechanical relay you end up needing LED bulbs all around the car, an electronic timer relay, and some sort of speaker to provide the clicking sound and those costs add up.
    – JPhi1618
    Feb 16, 2016 at 13:29
  • It is not a requisite they are LED bulbs; you can also control blinking patterns on incandescent bulbs using electronics!
    – sergiol
    Feb 16, 2016 at 15:52
  • 2
    A turn signal bulb will draw about 2 amps. There are at least 4 of them on a car, and with hazard lights on they all light up at the same time. That's 8 amps, probably closer to 10 amps depending on the bulb, wire losses, and the other two small indicator bulbs in the instrument cluster. I'm not saying you can't find a solid state, 10A relay, but they are going to be very expensive compared to tried and proven mechanical relay that has a cost of less than $1.
    – JPhi1618
    Feb 16, 2016 at 16:00
  • @JPhi1618 It amazes me why an electronic relay has to be expensive! Do you have sources of prices for them? In these days, when silicon chips are everywhere due to their low costs, why that? And I think producing one chip has costs; but reproducing it in millions is virtually costless! It is even more automatizable to produce integrated circuits, than mechanical parts, as instead of doing precision engineering for joining together moving mechanical parts, you will only cut a silicon wafer! And better, you could even do better, by integrating the blinking functionality on an ECU!
    – sergiol
    Feb 17, 2016 at 15:48

1 Answer 1


I can think of several reasons straight away:

  • Cheap
  • Easy to replace
  • Have a very distinctive click that makes it obvious when they are on, and when a bulb has failed
  • Are very well understood
  • Anyone can fit one without needing to understand much about electronics
  • Don't some BCM's have some indicator light features now? Feb 15, 2016 at 23:46
  • Yes, more and more are moving to on-board indicator circuitry. But still plenty of old-school relays :-)
    – Rory Alsop
    Feb 15, 2016 at 23:58
  • 1
    Indeed. It's comforting analogue sound that's emitted and surprisingly reliable. I think I had 320K miles on a Toyota 22R 4X4 and I never swapped a blinker relay. That's a lot of work for a bi-metal strip. Feb 16, 2016 at 0:05
  • 3
    A mechanical relay is cheaper and much more reliable than the newer designs being built into circuit boards. I have first hand experience of these circuit boards going bad and costing upwards of $200 when a relay would have been less than $100.
    – race fever
    Feb 16, 2016 at 0:06
  • 1
    On the topic of reliability. There is such a thing as good enough. Electronic relays may be able to be made more reliable than electromechanical ones. However, given that electromechanical relays almost never fail unless the powersupply is bad, why bother? they're good enough and cheap to manufacture. And a bad powersupply will kill electronic relays just as well
    – Leliel
    Feb 24, 2016 at 0:47

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