Why Is Your Ford F-150 Blinker Blinking Fast?- [Answered!!]

The F-150 Blinker can blink fast due to fused or near-fused bulbs. The relay switch might also be faulty and unable to control proper electricity flow. The turn signal light socket might become corroded and cause this problem. A faulty alternator or wiring problem might also be the reason.

But, there’s more to it. So, keep on reading to know all the details.

F-150 Blinker Blinking Fast: Reasons And Solutions

There are quite some reasons why your blinking light is behaving this way. First, let’s see them in the brief table below:

Fused or Near Fused BulbsReplace the Bulb
Faulty Relay SwitchReplace the Relay Switch
Corroded SocketClean Corrosion and Replace the Socket
Overcharging batteryRefurbish or Replace the Alternator
Faulty Ground Connection and WiringFix Faulty Wiring Connection

Now, let’s discuss them in detail.

Reason 1: Fused Or Near-Fused Bulbs

The most common reason for the blinker light to blink faster is fused or near-fused bulbs. In this state, the resistance of the electrical circuit changes. Thus, the turn signal lights go on and off at a certain pace. 

Solution: Replace The Bulb

If the bulbs are fused, you simply have to replace them. But, first, check properly if they are fused. First, activate the turn signal for the side blinkers you think are malfunctioning. Then, go around the Ford F150 and inspect the lights. 

If you can’t find anything wrong, activate the turn signal for the other side and inspect. It might also be that both blinkers aren’t working properly. You can also get the bulbs out and look inside the glass dome to check the filament.

If the filament is broken, of course, the light is fused. If it’s not, lightly tap the bulb. A proper filament shouldn’t vibrate after you tab the bulb glass. If it does, the filament is bad. Here’s how you can replace these bulbs:

Front Turn Signal Bulb Replacement:

Step 1: First, open the hood and locate the rubber seal beside the headlight. Unscrew and fold the seal back to access the lights.

Step 2: Locate the bolt underneath the rubber seal and two bolts on top of the headlight. Unscrew all three of them. 

Step 3: Pull the headlight out gently while removing the connections. Then, locate the turn signal light. Pull the turn signal light out by turning it counterclockwise. 

Step 4: Take your new turn signal light and insert it in the previous spot. Turn it clockwise half a turn to install it.

Step 5: Put the headlights back on. Then reattach the bolts and the rubber seal. And, you’re done!!

Rear Turn Signal Bulb Replacement:

Step 1: Open the tailgate and locate the light protector panel. It’s a plastic cover for protecting the lightbulbs. Unscrew the bolts on the panel’s sides.

Step 2: Pull out the protector panel and locate the faulty bulb.

Step 3: Turn the bulb counterclockwise to pull it out. Take the new bulb and attach it to the previous position by turning it clockwise. 

Step 4: Reattach the protector panel and its bolts. Finally, close the tailgate and you’re done!

After the installation process, check to see if the blinkers are functioning properly now.

You can also watch this video for help:

 Also, be sure to check which lights are appropriate for your lighting system. You should find it in the owner’s manual of your vehicle.

You can also get the light replaced by a professional. On average, it’ll cost you about $80-$110 in total. 

Reason 2: Faulty Relay Switch

The next possible reason is a faulty relay switch. There are different relay switches for different functions in a vehicle. They ensure that too much current doesn’t flow through the component. 

But, over time, the relay switches go bad. Thus, they can’t efficiently control the flow of current. Thus, you see the blinkers blinking faster than they should. 

Solution: Replace The Relay Switch

If the relay switches are bad, replace them with new ones. First, you have to locate the right relay switch in your fuse box. 

In the F150 19917-2003 models, the fuse box is near the brake pedal left to the steering wheel. In 2004-2022 models, it’s located on the right side underneath the glove compartment. 

Look in the owner’s manual to determine the relay switch number for your blinkers. Find it in the fusebox. Then, you have to test it before replacing it. 

If you have an extra switch of that number, replace the suspected relay switch with it. If the blinkers start working properly, the previous relay switch was bad. Thus, replace it with a new one. 

You can also test the relay switch with a multimeter. A good relay should display a resistance of about 50-120 ohms. If it’s out of this range, replace it with a new one. If you don’t know how to use a multimeter, watch this video: 

You can also get the relay replaced for $60-$120 by professionals. 

Reason 3: Faulty Socket

Next, the sockets that the bulbs fit into might also be faulty. Over time, corrosion builds inside the sockets. Thus, the electricity flow is disrupted and the blinker blinks abruptly. The wires inside the sockets might also be broken or corroded, creating the issue.

Solution 1: Clean Corrosion

If the socket is corroded, cleaning it should do the trick. Just remove the socket for the turn signal light. Wear a safety glass and spray some cleaner on the socket terminals. White vinegar can be used as a cleaner. 

Clean Corrosion
Source: www.youtube.com

Then, take a small screwdriver or pick and clean out the corrosion. Be sure to clean gently so you don’t damage the terminals. Repeat this process until the socket is corrosion free. Finally, wipe it off with a cloth. 

Solution 2: Replace The Socket

If cleaning the corrosion doesn’t work, most probably the socket itself is bad. Ford F150 sockets are available in different types for different purposes. Some common socket sizes are listed below:

  • Spark plugs: A 9/16-inch socket end is used on the Ford F-150 spark plug socket.

It is therefore preferable to use a 21mm socket with lug nuts on a Ford F150 over a 12-point socket with spark plugs.

You can check the socket by using a multimeter. Here, turn on the multimeter and turn the dial to check resistance (Ω). Attach the probes of the multimeter to the grounds of the socket.

On the standard sockets, the ground terminals are the bottom two terminals. And, on CK-type sockets, the left two terminals are ground. If the socket is good you’ll get a reading of less than 1 ohm.

But, if the socket is bad, you won’t get a reading. So, you can go ahead and replace the socket. Here, you can watch this video for assistance: 

Here, first, test the socket if it’s bad with a continuity tester. Attach its clip to the black wire to touch the probe on the metal tab of the socket. 

Remove the turn signal light like before and disconnect it from the socket. Disconnect the socket from the wiring harness and replace it with a new one. 

Reason 4: Overcharging Battery

Next, the voltage regulator of the alternator in your Ford F150 might also be bad. The alternator recharges your battery by converting mechanical energy to electrical energy. But, if the voltage regulator is bad, it’ll overcharge your battery. 

Thus, the components powered by it such as the blinkers start malfunctioning. Common signs of this problem include a swollen and leaking battery. It might get excessively hot. The lights seem to be too bright and they blow out faster. 

Solution: Refurbish Or Replace The Alternator

If the alternator is bad, you can simply refurbish or replace it. Sometimes, a few of the internal parts like the alternator of the alternator get damaged. Just replacing them should get the alternator running. 

A fixed alternator also lasts for another four to five years (50000-100000 miles). You might also get a 90-day warranty on the fixed alternator. You can further cut down the costs by fixing it yourself. 

Here, you can follow this video for a detailed guide:

If the alternator is too bad, just replace it. If it’s too complicated for you, take it to a professional. He’ll replace the alternator for approximately $350-$400 in total. 

But, in case of overcharging, replacing only the voltage regulator should fix the issue. First, take out the alternator from your Ford F150. Then, follow these steps:

Step 1: Get the top of the alternator out by removing the bolts with a socket and wrench. Remove the screws with the screwdriver. 

Step 2: After taking the top off, locate the voltage regulator. It’s also attached with screws. Take them off and the regulator should come out. 

Step 3: Now, test the voltage regulator to make sure it’s malfunctioning. If it is, proceed to step 4. 

Step 3: Take the new voltage regulator and screw it in. Reattach the top by attaching the bolts and screws. 

With that, the voltage regulator should be fixed along with the overcharging issue. 

Reason 5: Faulty Ground Connection And Wiring

If the ground connection of your battery is bad, it may also cause a problem. The wires connected to your turn signal lights might also be corroded or loose. Thus, the blinker might blink abnormally.

Solution: Fix The Connection

Carefully inspect the ground connection of your battery and the other wires. Here, you can use a multimeter.

 Attach the black probe of the multimeter to the negative battery terminal. Attach the positive probe to any part of the Ford F150’s frame. If the voltage reading is near zero, the ground connection is fine. 

If it’s not and some wires look corroded, replace the wires to form new connections. If they’re loose, just tighten them with electrical tape or wire connectors. Although, using wire connectors is better than electrical tape. 

If you can’t find the faulty wire, contact a professional.  


What Causes Turn Signals to Blink Slowly? 

Turn signals blink slowly mainly due to burnout or incorrect bulbs. When the bulbs are defective, the flasher takes longer to heat up. Thus, the circuit takes longer to brake. Thus, the flash rate becomes abnormally slow. 

Why Is Blinker Constantly On?

Blinker stays constantly on due to a failed wiring or connector. Here, check both the power and ground of the connector. Although both turn signal bulbs have the same ground point, the wiring can be faulty particularly. 

How Long Can A Blinker Last?

A blinker might last for about 4000 hours. Although, it might be different according to the model. Check your owner’s manual for a more specific time limit. 


Hope now you’re clear about why your Ford F-150 blinker is blinking fast. Still, we’d like to mention one last thing. Get your blinkers fixed as soon as possible. Because fast blinkers (more than 120 times per minute) are considered illegal. You might get pulled over for it. Thanks for reading our whole article. 

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William Baldwin

This Is William Baldwin, The Founder & Managing Editor of this website. Me and my team share automotive tips, tricks, and news

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Talha Atta

Talha Atta, a Mechanical Engineer and experienced technical content writer and editor at Autoglobes.com with a passion for the automotive industry.