Why Does My Turn Signal Blink Fast?

Ah, that feeling when the blinker syncs up perfectly with the song filling the cabin. But wait, why does my turn signal blink fast all of a sudden? How big a problem is this, and what are the possible solutions?

Blink on, Blink off

The turn signal circuit is relatively straightforward in most vehicles: Power runs through a fuse from the battery to a turn signal relay. When you select a turn signal direction at the wheel, you complete the control circuit, activating and sending power through a secondary load circuit. This secondary circuit includes the bulbs intended to light up when the signal direction is selected. But, of course, you don’t want the bulbs to be constantly lit, so the power goes through a flasher.

Flashers — of which there are different types — are usually designed with a small strip of metal whose shape is highly susceptible to heat. Current flowing through the strip causes the metal to heat and cool by bending and straightening to complete or break the circuit. So, the flasher is temperature controlled and designed specifically to bend at exact intervals based on electrical conditions.

Why Does My Turn Signal Blink Fast?

The current is determined in part by load demand, aka, the bulbs. Although the circuit is simple enough, it’s designed with precise calculations for the circuit’s voltage, current and resistance. Altering any of these factors can cause a change in blinker speed.

Bad to the Bulb

A bad bulb is by far the most common reason that a signal blinks faster. This is because a bad bulb alters the resistance in a circuit, sending a different current through the blinker.

To figure out if this is the issue, test all signal lights to see if any bulbs are visibly out. Otherwise, inspect each turn signal bulb for signs of failure such as broken filament or dark, clouded glass. Replace any bad bulbs you find and retest the lights.

Poor Lighting

Aftermarket parts that don’t match the designed system can also affect the blinking speed, so be sure to replace any duds with the right parts. Avoid replacing halogen bulbs with LEDs and upgrading to aftermarket parts that add additional lighting or don’t factor the blinkers into account. If you haven’t recently done any work on the lighting system, an incorrect part isn’t likely the problem.

Bad Connection

Wiring that’s corroded, fried, worn through the insulation or loose at a connection point will affect the resistance and blinking speed. Look out for bad ground connections. Relays and flashers can go bad with time, water damage, excessive heat and other environmental stresses. These components are relatively easy to replace, and doing so can quickly rule them out as the fault. Again, just remember to replace like with like.

A fast blinking turn signal isn’t a reason to panic, but it does suggest something is wrong with the circuit. Luckily, the fix is relatively painless once you know what to look for.

Check out all the turn signal products available on NAPA Online or trust one of our 17,000 NAPA AutoCare locations for routine maintenance and repairs. For more information on turn signals, chat with a knowledgeable expert at your local NAPA AUTO PARTS store.

Photos courtesy of Blair Lampe.