test a relay terminal

Relay is the most used component for controlling in car and other machines. If your device is not working properly there are chances of fault in relay. For that you might will hire a electrician and this will cost you some dollars. But you don’t have to worry about any thing because In this article I will show How to Test a 5 pin relay with a Multimeter.

Before we get in to the topic first of all we will discuss a little about relay and multimeter.

What is Relay?

5 pin relay

Relay is an electronic device installed in the electrical system of machines and different vehicles. The function of relay is to allow a low current circuit to control one or more loops of higher current. Also, It isolates the high voltage circuits and protects the small current circuit by bringing in an electromagnetic coil to control the course.

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What is a multimeter?


A Multimeter is a tool for measuring electrical quantities like resistance, voltage, and current. All these meters (ohmmeter, voltmeter, and ammeter) that measures those quantities are combined to a single meter is known as multimeters. There are two types of multimeters:

1.Analog Multimeters

Analog multimeters work on the principle of moving coil meters. These meters use the deflection of an indicator needle to indicate the level of the measurement on an analog display.

2. Digital Multimeters

The usage of pins of 5-pin relay are

  • Two pins that control the coil
  • Other Three pins will switch power between circuits

The three pins have both NO (normally open) and NC (normally closed) connection pins. While the two pins that control the coil activates. There are following steps involved to test a relay to see if it is bad.

1. Testing the relay’s coil

 test relay with multimeter

To test the relay’s coil we must have resistance and tolerance of coil, that we can get from the data sheet. If the resistance and tolerance value for certain relay is 500Ω ± 10%. In this case our resistance will be between 425Ω – 575Ω.

Now, Adjust multimeter knob to ohmmeter settings and connect both probes to it. As polarity doesn’t matter in case of resistance so we can use any probe at any point. Now note the resistance on screen.

  • if the readings are in range than your coil is fine.
  • Also, if the readings are out side the range, i.e., very high or very low, then the coil has a problem.

Keep in mind the coil is not repairable, so replacing is only option. This is the most important step in testing a car relay with multimeter.

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2. Test a 5 pin relay terminal

test a relay terminal

As we are done with coil testing, now its time to test the resistance between the terminal of relay. The terminal of the relay are

  • Normally open terminal
  • Normally closed terminal
  • Common terminal

Normally open terminal Testing

For testing of the normally open terminal follow these steps

  1. Set the multimeter knob to ohms
  2. Connect one of the probe of the multimeter to the COM terminal while other probe on the normally open terminals.
  3. Don’t worry about polarity because it doesn’t matter while measuring resistance.
  4. Note down the reading from multimeter screen.
  5. The resistance between COM and the open terminal should be high as the two are not connected.
  6. Also, if the reading on the screen shows a continuity, i.e., a zero resistance, then the terminals are faulty.

Normally closed terminals Testing

For normally closed terminal

  1. There should be no voltage closing.
  2. The resistance between the COM and normally closed terminals should be zero ohms or very close to zero.
  3. At zero ohms normally closed terminal should be working fine.

For testing of the normally closed terminal follow these steps

  1. Adjust multimeter knob to ohms
  2. Place one knob of multimeter on normally closed terminal while other on COM terminal.
  3. Don’t worry about polarity because it doesn’t matter while measuring resistance.
  4. Note down the readings on the multimeter screen.
  5. If the resistance shown is zero then relay is fine
  6. like wise, In case there is a high resistance between the normally closed terminal and COM, then then relay is faulty.

Testing the common terminals

On 5 pin relay the common terminals is labeled as 85 and 86.There should be very low resistance between the two terminals.
These steps should be followed for the testing of the normally closed terminal

  1. Rotate your multimeter knob to ohm.
  2. Place the one probe of multimeter on 85 pin.
  3. Also, place the other probe on 86 pin.
  4. The resistance should zero or very low.
  5. If the meter shows the zero or negligible small resistance then common terminal is fine.
  6. Similarly if the meter shows the high resistance then common terminal is faulty.

Relays are complex unlike other instruments like fuse. Fault detection is difficult in case of relay.

This article has guided you in detail on “How to Test a 5 pin relay with a Multimeter?”. I am sure now you can test on the 5-pin relay with multimeter. we have tried to cover each aspect of relay testing using Multimeter and look for more and tried to cover that in next update. Do you have any question? Let us know in the comment section below


By inham

Inhamullah Jadoon is an Electrical Engineer and Co Founder of geekyengineers.com. He has vast amount of experience in the field of Engineering and in assisting Engineers on Software and Hardware issues.

2 thoughts on “How to Test a 5 pin relay with a Multimeter?”
  1. Thank you for the information. And most makes sense, however there are a few things which are confusing.
    No mention of a power course. Are you using a battery? A 12 volt power source?
    Also, why do you show a diagram with ONE COM terminal, but when in the section to test COM terminal you say there are more than ONE COM terminal?
    Lastly, would I attach a power source to the terminal of the induction coil to test the switching ability of the relay from NC to NO?
    Thank you again.

    1. Usually 3-pin relays have a common (COM) terminal and two additional pins for normally open (NO) and normally closed (NC) contacts.
      But some relays may have multiple COM terminals. In this case you have to determine which COM terminal corresponds to the circuit you are testing. This can be done by tracing the wiring diagram for the relay or by using a continuity tester to identify which pins are electrically connected.

      You can use 12V battery or Dc power supply for testing.

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