How does a blinker in automobiles work?

Answer 1

There is a flasher unit, wired in series with the circuit for the turn signal indicator bulbs.

Inside the unit, the current for the lamps, is passed through a wire wrapped around a bi-metallic strip. The heat from the current causes the strip to bend. The bi-metallic strip has contacts at one end, the bending breaks the circuit and turns the lamps off. The strip cools and remakes the contact, turning the lamps back on. This is repeated until the turn signal arm is switched back to off.

The switch contact is on a rocker which enables the switch to act quickly and cause an audible 'click', so you can hear the signal as well.

This has the added advantage of giving a warning that one of the bulbs has failed. The front and back turn signal lamps are wired in parallel and draw enough current to operate the flasher unit properly.

If one lamp fails, the current is halved. The flasher unit does not get enough current to heat the bi-metal strip properly. The indicators then flash quickly and erractically, indicating that a bulb has failed.

Having said all that, modern cars are increasingly using electronic circuits, in place of the bi-metallic strip, using transistors and IC's to make an astable mulivibrator, which switches the turn signals on and off.

This enables electronic control of the signal lamps, smaller signal wiring to the control stalk, automatic cancellation and electronic noise as an alarm which can change volume, if left on. Electron flasher units also run independant of current, so can power new LED lighting, without affecting performance.