Turn Signal Flashers

The turn signal flashers is what is responsible for the blinker light turning on and off. It is also responsible for the speed the light flashes. Often when people have problems with their turn signal they think back to the old days when the most common cause was a bad flasher.

Picture of turn signal flasher

Turn Signal Flasher


This device is used in both the hazard warning lights and the turn signal systems. The turn signal flasher itself will look different depending on the year make and model of the vehicle. General Motors vehicles most commonly use an aluminum cylinder type housing to contain the flasher assembly.

Ford and some other foreign car manufacturers make their flasher assembly look like a standard relay. In either case they contain a temperature sensitive bimetallic strip and a heating element. This bimetallic strip is connected to one side of a set of contacts.


Voltage from the fuse panel is connected to the other side. When the turn signal or hazards are activated current flows through the flasher unit and turns on the bulbs. The current flowing through the flasher causes the heating element to emit a large amount of heat which in turn causes the bimetallic strip to bend and therefore open the circuit.

When the current is disconnected it allows the bimetallic strip to cool. Then it will automatically close the circuit to illuminate the bulb once again. This intermittent on-off interruption of current flow makes the turn signals work correctly and notifies other drivers that you are turning.

Where are turn signal flashers

Picture of GM flasher

GM Flasher

On many current model vehicles and trucks you can find the turn signal flasher mounted in the fuse panel. On older vehicles this may not be true. The turn signal and hazard flashers can be mounted in various locations under the dashboard. In some cases this is so the audible clicking can be heard by the driver to let them know the flasher is operating.

You can use this sound when they are functioning properly to track down the location of the turn signal flasher. When the turn signals or hazards are not working finding the flasher can be more difficult. I recommend that you get a quality online service manual that will provide pictures of the component location.


Turn signal problems

Picture of turn signal switch

Turn Signal Switch

Keep in mind that you may have a problem with the turn signal flasher but it is far more common when turn signals and hazard lights are not working that there is a problem with the bulbs or sockets. Again in a service manual you can follow a diagnostic tree chart to get to the root of the problem.

The turn signal and hazard systems are designed to operate a specific number of bulbs. If one of those bulbs has an open filament and is not working the turn signals may flash faster than normal and on some models may flash slower or not work at all. It is always a good idea to start by checking the operation and verifying that all of the bulbs are okay before you move on to checking the turn signal flasher.

Although it is not as common, problems with the switch are also one of the possibilities. If you’re flasher tests good and all of the bulbs are working properly it may be time to check the turn signal switch itself. And the same thing goes for the flasher switch. Note on some models like the mid nineties Pontiac Grand Am the turn-signal switch is a common problem.

When it comes to electrical diagnosis it is a good idea to follow a set path and confirm failed components before you replace them. An automotive meter is an inexpensive and handy item to have in your toolbox. For more information about common auto repairs this next link will take you back to the main page for the blog about auto repair.


2 comments

  1. My left and at times right tail lights will not go off causing the battery to drain on my 88 GMC 2500 pick up. At times a slight touch of the turn signal lever will temporarily turn off the offending tail light. What should I repoace? How? Thanks.

  2. On older Chevy pickups I have seen both the brake light switch and the turn-signal switch fail and cause the tail lights to stay on.The difference is that the turn signals should not operate with the key off. The brake lights on the other hand will come on with the key out of the ignition as they are powered straight to the battery. Both the turn signal switch and brake light switch are common problems on older Chevy pick ups and neither one costs to much. As far as the replacement procedure I recommend a manual for your year and specific model for the step by step instructions.

Leave a Reply

Your email address will not be published. Required fields are marked *