flasherrelay

A flasher relay, or turn signal flasher, is an electrical device in vehicles that controls the on-off cycling of the turn signal and hazard lamps. Its primary function is to produce the characteristic blinking required to indicate turns or warn other road users.

Historically, most flasher relays were thermal devices. A small heater inside the relay powered by the turn-signal circuit warmed a bimetallic strip, causing it to bend and break the circuit. As the strip cooled, the contacts reclosed, repeating the cycle. The flash rate depended on current draw; a burned-out bulb or added load could alter the timing. Modern designs increasingly use solid-state electronics to generate blinking, offering more consistent timing and the ability to sense load and adjust the rate accordingly.

Flasher relays come in various configurations, most commonly three- or four-pin units. Some vehicles place the relay in the fuse box or routing modules, while others have it integrated into the body control module. The exact wiring and placement vary by manufacturer and model.

Compatibility considerations include bulb type and load. Incandescent bulbs typically work with standard flashers, but upgrading to LEDs often requires a compatible electronic flasher or load resistors to maintain proper timing. In many cars, a failure of the flasher or a burned-out bulb is indicated by abnormal flashing, such as hyper-flash when a lamp is out.

Flasher relays are standard components in automotive lighting systems, though their specific design, location, and integration approach differ across vehicles. They may also be used in other timed switching applications beyond automotive signaling.