How to Test a Car Relay With & Without a Multimeter

How To Test A Relay With Multimeter

In a car, the relay is an electrically operated switch that is used to control a circuit. The switch consists of a coil of wire that is wrapped around an iron core. When the coil is energized, the iron core becomes magnetized and attracts a movable contact that is connected to the load. The load can be either an electrical device or a circuit.

There are a few ways to test a car relay. One is to use a multimeter to test the resistance of the coil. Another is to use a test light to see if the relay is getting power. The third way is to use a voltmeter to see if there is voltage coming from the relay.

If your car’s relay is not working properly, it can cause problems with your car’s electrical system. There are a few ways to test a car relay. If you’re wondering how to test a car relay with & without a multimeter, then look no further! in this powerful article, You’ll learn how to test a car relay with & without a multimeter.

How to Test a Car Relay With a Multimeter


There are two ways to test a relay using a multimeter.

  1. Testing A Relay Using Voltmeter
  2. Testing a Relay Using Ohmmeter

1. How To Test A Relay With Voltmeter

How To Test A Relay With Multimeter
How To Test A Relay With Multimeter
  1. Take a 12 volts battery, connecting wires, and a voltmeter or a multimeter and set it to the volt measuring.
  2. Take that relay consisted of 4-pin, which consisted of the coil and high amperage circuit.
  3. Check the voltages of the battery first, with the voltmeter.
  4. A voltmeter can be used to test the relay. First, energize the relay. You will hear a clicking sound. It means that terminals 85 and 86 are fine which produces a clicking sound. That click just means that the coil circuit is working fine, but it never means that the relay is in its best condition.
  5. Now, we will test the relay’s high amperage circuit. Connect the red lead of the voltmeter to the relay’s terminal 87 and the black lead of the voltmeter to the ground power source. At this time voltmeter will show a reading of 12-volt while by de-energizing the relay, the voltmeter should read zero volts.

Apart from this you can set the multimeter to the “Continuity” scale and listen to the beeping sound.

2. How To Test Relay With Ohmmeter

Testing A Relay Using Multi Meter
Testing A Relay Using Multi Meter

For further checking and confirmation for the testing of the relay, do check the resistance of the relay with the ohm meter.

  • Take the voltmeter and place it in the ohm (Ω) reading and set the lowest range of the ohm scale.
  • Take a four-pin relay, which has the two most significant circuits, coil, and high amperage circuit.
  • Before energizing the relay, connect the ohmmeter leads to a high amperage circuit of the relay. Your ohmmeter should read infinity (0L, Open Circuit).
  • Now, energize the relay, and you will hear a clicking sound. It means the relay’s coil circuit is working.
  • Now, after energizing the relay, your ohmmeter instead of infinity should detect zero ohms or any resistance value in the number of hundredth or thousandth. Or you can also check the continuity of the beep sound.

This is an Info
Be cautious do not use an ohmmeter on a live wire. It can damage the ohmmeter while testing the resistor when the current is flowing. Here I am talking about the high amperage circuit of the relay. Do not use an ohmmeter when the high amperage circuit is connected to the battery.

This is an Info
The high amperage circuits of some relays are Normally Closed (NC) and should open by energizing the relay. So, be careful to check the relay diagram before testing. Usually, these kinds of relays are marked 30 and 87a terminals.

Testing Relay’s Coil Circuit

The resistance of the coil circuit is approximately 50 to 120-ohm value between coil circuit pins. If it is less than 50 ohms, it could be faulty.

How To Test A Relay Without A Multimeter

Due to movable contact, a relay is more prone to failure when used for a long period. Too much current can also cause relay failure. Diagnosing a faulty relay is not a hard task. In this tutorial, I will show you a step-by-step procedure on how to test an automotive relay without a multimeter.

One thing you need to know about testing a relay is that the basic procedure of testing every relay in a car is the same. Whether that is a fuel pump relay, Starter motor relay, Car Air Conditioner relay, Headlight relay, radiator fan relay, or horn relay. Don’t be afraid.

I will take the horn relay as a sample to help you understand it in a better way. Suppose your car horn does not work.

Car Horn Does Not Work

Horn Beep
Horn Beep

Here I will show you in seven steps how to figure out the fault when the horn does not work.

Step 1. Check The Fuse First

Fuse Testing
Fuse Testing

Before checking the relay, it is wise to check the horn fuse. The fuse schematic is usually printed on the inside of the fuse box cover or sometimes outside of the cover.

Step 2. Locate And Listen To The Clicking Noise Of The Relay

Testing Relay
Testing Relay

First of all, check the relay location. Fuse box comes in many different locations. It comes under the hood, under the dashboard, or side kick panel.

But usually, a car horn relay comes under the hood fuse box. Once a relay is figured out, have a helper beep the horn and touch the relay if it makes a clicking sound.

If so the relay is working fine. In this case, the horn might be faulty or have a wiring issue. If the relay does not make a clicking sound, then proceed to the next step.

This is an Info
Sometimes a relay makes a clicking sound but still can be faulty. This is because too much carbon is built upon the relay’s high amperage circuit’s contacts (Terminals 30 and 87). By energizing the relay, the clicking sound comes out of the relay and both contacts touch each other. But due to too much carbon buildup, the current does not flow.

Step 3. Remove Relay From The Fuse Box

Extracting Relay
Extracting Relay

Now, it is time to remove the relay from the fuse box for inspection purposes. Smoothly grasp and pull the relay upward by hand while slightly wiggling the relay for gentle extraction.

Step 4. Visually Inspect

Corroded Relay
Corroded Relay

Before you start making any test, first visually inspect the relay, and look for corrosion and carbon deposits. Check the relay pin connector and fuse box female connector of the related relay.

Make sure the connectors are clean. Sometimes overheating prevents proper current flow in a circuit.

Step 5. Identify Relay Terminals

Now you have to identify the relay’s terminals. Find out which terminal belongs coil and load circuit. Some relays have a diagram printed on the case itself to identify pin terminals.

Step 6. First Test The Horn

Horn Checking
Horn Checking

Before you test the relay It is good to check the horn. Make sure you have a good working horn.

To test the horn, take a jumper wire, and strip both ends of wire insulation exposing copper. Connect one side of the jumper wire with a 12-volt positive battery source and put the other side of the wire in 87 female connectors of the horn relay in the fuse box.

Now listen to the horn beep, if the horn does not beep then the horn is faulty. If the horn does beep sound then precede further to test the relay.

Step 7. Check The Relay

Now, it is time to test a relay. First of all, have two jumper wires (if possible fused wires). Connect one side of both jumper wires with battery +ive and -ive terminals and connect the other side of both jumper wires with the relay’s coil circuit. Check for the relay clicking sound.

If the relay does not produce a clicking sound, then the relay is faulty. If it does produce a clicking sound then check for high amperage circuit.

Put a load (Light Bulb) in the relay’s high amperage circuit, the bulb should illuminate. If the light bulb illuminates, then the relay is correct. If it doesn’t, then the relay is faulty.

Step 8. Replace The Relay

While replacing a bad relay make sure the new relay is in good condition and that also terminals match with the old relay.

Final Note:

If all tests prove that the relay is correct and still the horn does not work. Then check the wires, corroded terminals, loose connections, disconnected wires, or the accessory itself to be faulty. All of those conditions can cause your circuit to fail.

The Fastest Way To Test A Relay

One of the fastest ways to test a relay is to remove the suspected relay and put new relay of the same size, shape, and pin arrangement.

Check if the accessory works, if yes. Then the old relay is bad.

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