Secret Diagram

The trafficating system in an automobile generally consists of two blinkers in the front and two blinkers at the rear, and their will be a small monitor lamp on the dash board for drivers indication. The blinker lamps are 12V, 18W rating and the monitor lamp is 12V 1W rating, a high power Alloy junction pnp transistor AD149 is used in this circuit. The blinking rate is 90 times per minute.

This circuit is suitable for installation in vehicles having 12v supply. The transistor Q1 and Q2 forms the basic multivibrator with a triggering frequency of about 90 pulses per minute; transistor Q3 performs the function of the switch. There are interstate coupling arrangements between the multivibrator, the switching stage and the monitor stage.

Source - http://www.electronguide.com/circuits_pages/AutomobileIndicator.html