A three-pin flasher relay works on principles of electromechanics to appropriately power turn and hazard signals on most automobiles manufactured since the late 1930s. Historically, turn signal systems evolved from relays and mechanisms to solid state apparatuses. All flasher relays have an audible and visible output when connected as designed.
A flasher relay is powered off of the automobile’s 12-volt DC main. It is grounded (positive or negative ground) to match the rest of the car’s electrical system. Its circuit is designed for a maximum current load to power the turn and emergency signals only. Any further demand or overload will trip a circuit breaker or blow a fuse or fusible link.