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How to Test a Flasher Relay with a Multimeter

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A flasher relay is a type of electrical switch that controls the blinking of turn signals and hazard lights on a vehicle. When the turn signal or hazard light is turned on, the flasher relay activates the bulbs by sending an electric current to them. The bulbs will then blink at a set rate until the turn signal or hazard light is turned off.

Top 5 Indicators You Need to Replace Your Flasher Relay

1. Your turn signals or hazard lights are not working

2. Your turn signals or hazard lights are working, but they are not blinking

3. Your turn signals or hazard lights are blinking too fast or too slow

4. There is a clicking noise coming from the dash area when you activate the turn signal or hazard light

5. The flasher relay itself is hot to the touch

If you notice any of these indicators, it is likely that your flasher relay needs to be replaced. A faulty flasher relay can cause many problems and can even be dangerous, so it is important to replace it as soon as possible.

Also note, if you notice your indicators flashing twice the normal speed, this is likely a bulb issue not a flasher relay problem. Often if a bulb on one side has blown then the other will flash at twice the speed as the load is far greater due to the increased energy. In this case replace the bulb first.

How to test a flasher relay with a multimeter

To test a flasher relay with a multimeter, first locate the relay. It is usually located in the dash area near the fuse box. Once you have found the relay, remove it from its socket and set it on a firm, flat surface.

Next, use your multimeter to test the continuity of the three terminals on the relay. The continuity setting on a multimeter will make a beeping noise if there is a complete circuit between the two points that you are testing. If there is no continuity, then there is an open circuit and the flasher relay needs to be replaced.

You can also test the resistance of the terminals on the flasher relay. The resistance setting on a multimeter measures the amount of resistance in a circuit. A low resistance indicates that there is a good connection between the two points, while a high resistance indicates that there is a poor connection. If the resistance is high, then the flasher relay needs to be replaced. While s flasher relay may still work with high resistance it will likely not get all the power to the bulbs.

Steps to test a flasher relay

Step 1. identify the terminals on the flasher relay. If it’s a common three prong relay it will have 3 terminals:

  • Battery terminal (B)
  • Load terminal (L)
  • Panel or dash-indicator terminal, also referred to as ground (P)

It’s worth noting some flasher relays may be set out differently or may not have three prongs. However when testing the same principals apply.

Step 2. Next, with the key in the ON position, check if there is power at the B terminal. If there’s no power or 12V, then the problem might be a blown fuse or a bad connection to battery power and not an issue with the flasher relay.

Proceed to check if there is continuity between the L and P terminals while someone activates the turn signal. If there’s no continuity, it means that either the flasher relay is defective or there’s a break in the wiring between those two terminals.

There should also be continuity between the B and P terminals when someone activates the hazard lights. If not, then it points to a problem with either the relay itself or the wiring to the hazard light switch.

Note this will only work while the turn signal is activated. If it works when the turn signal is not activated then the relay is broken as this would mean the bulb stays on all the time.

Replace the flasher relay if testing shows that it’s defective.

Step 3. Turn your multimeter to the ohms setting, and then click the test probes together. You should see a reading of zero on the multimeter display. This means there is continuity between the points and the multimeter is working properly. Now try this on the flasher relay.

Step 4. Next, put the test probe on the P terminal and the L terminal. Again, turn your multimeter to the ohms. You should see a reading of zero on the multimeter display. This means there is continuity between the points, and the flasher relay is working properly.

Test this for L and B also to confirm that the overall flasher relay is functioning correctly, if your multimeter doesn’t return a zero or a beep this means that the fuse inside the relay may be blown as it cannot make a connection between the two points. This is a good way to find out quickly if the flasher relay needs replacing.

Now just because those all work that doesn’t mean the relay is working properly. There might be issues with the speed of the flash or being too fast or too slow. To test this connect the flasher relay up to a battery with the power passing through your multimeter.

This test is a little more involved and requires some extra equipment. This tests the flash rate of the flasher relay to see if it’s working correctly.

You will need:

  • 12V battery
  • test light
  • resistor (1kohm to 10kohm)
  • Alligator clips

First, connect the alligator clip to the positive terminal of the battery and then touch the other end of the alligator clip to one end of the resistor. Next, take the other end of the resistor and touch it to the positive terminal of the test light. Finally, take the other end of the test light and touch it to one of the terminals of the flasher relay. It doesn’t matter which one as long as it’s not the ground.

What you are doing here is setting up a circuit with the battery being the power source, the test light being the load, and the flasher relay in between controlling the flow of electricity. This will allow you to see if the flasher relay is working correctly.

Now, activate the turn signal or hazard lights. You should see the test light come on. If it blinks at a steady pace, then that means the flasher relay is working correctly. However, if it blinks erratically or not at all, then that means there might be an issue with the flasher relay.

You can also use this test to see if the flasher relay is working correctly with a multimeter. Just set your multimeter to the AC voltage setting and touch the leads to the two terminals of the flasher relay. You should see a reading on the multimeter. If the reading fluctuates, then that means the flasher relay is working properly. However, if there’s no reading or the reading is very low, then that means there might be an issue with the flasher relay.

With these tests, you should be able to determine whether or not the 3 pin flasher relay is defective. If it is, then you will need to replace it.

Conclusion

In this article, we have gone over how to test a 3 pin flasher relay with a multimeter. We first went over how to test for continuity to see if the overall relay is working. Next, we went over how to test the flash rate of the turn signal or hazard lights. Finally, we went over how to use a multimeter to test for AC voltage fluctuations. With these tests, you should be able to determine whether or not the flasher relay is defective.

Toby Ashby

I am an automotive specialist with over 20 years of experience in and around electronics