eg. The polarity of probes on terminals doesn’t matter because we are finding resistance. The first step on how to test a relay is to determine the relay terminals and it's function. Check the Relay’s Coil Terminals Using a Multimeter: To check the relay whether it’s good or faulty one, we need to check the resistance of a coil. Then select the high beam with the dimmer switch. Also check for discontinuity between N/C contacts and pole. in the case of a light bulb) or take it to be repaired. In this article, we will show what resistance readings you should get when you measure various points of a relay. Therefore it's usually located close to the Battery & Headlights (Engine Compartment) Good Luck THE BEST Multimeter tutorial HD RELAY BASICS Relay … If the multimeter is set on continuity mode, it will produce a beeping sound. Put your digital multiple at the lowest range on the Ohms scale or put it in continuity. Your multimeter should register 0.2 to 0.9 Ohms. Touch the black probe to one screw and the red probe to another. Connect 12 V supply to Control pins on the relay and listen for a physical click (Gross Test). if the bulb lights, it means the relay is working. Hold the black probe against the negative terminal and the red probe against the positive one. The voltage at the low beam connection should be 0 volts and at the high beam connection should be 12.4 volts. Again, one should read 12 volts. Put the multimeter in the ohmmeter setting; Place one of the multimeter probes on the NO terminal and the other on the COM terminal; Read the resistance; If the resistance value is around several … The first method of checking the terminal resistance was useful when you have datasheet available, and another method was also useful when you are making a project based on a relay or you do not have any datasheet available then you can use that method. No continuity should register. Then connect a pin to one of the pins of the power circuit, and connect the other pin to the other power terminal. Most vehicles use several interchangeable relays in the same box; check the number stamped on top to make sure they the same before you start pulling them. If you get the resistance value of 0Ω, congratz this terminal is working correctly. Orient the relay so the middle -- noted "87a" -- terminal post is vertical to you, and the "sideways" 30/51 post is on the right. If you don’t hear the click, your relay is probably bad. This will work on all light sockets, from the one on the wall, to the one on the lamp. Probe the main wire leading from the relay with the test light. In the measurement of NO contact there should be the resistance of MΩ, if you find the value of MΩs then this NC terminal is working fine, and the reason behind this is that when NC and COM are not connected there is a huge amount of impendence. De-energize (remove B+) the control You will find the resistance of the relay coil. In this article, we will see what resistance readings are required to declare that the relay you are using is the good or defective one. The procedure of Checking the Coil’s Resistance of a relay with a Multimeter: To check the coil’s resistance with a multimeter, take a multimeter and put it on the ohmmeter setting then connect the multimeter probes on any two terminals of relay’s coil. Pull the relay out of its socket and check across the coil with the ohmmeter section of the multimeter. If you’re attempting to test live wires, find the screws pinning the wires in place. How To Test a Relay with a Multimeter Step by Step guide, Check the contacts of relay with a multimeter, Common Base Amplifier, BJT Transistor Common-Base Amplifier. How to Check That Power is Getting to the Headlights: Use a Test Light. A 12v Test Lamp or Multimeter would be useful here! Determine relay number and pin out. Place the multimeter’s one probe on NO terminal and other on COM terminal. For that, we need a relay datasheet, in which all relay detail described. If not, the headlight … If you hear the relay click, you know the coil is working, but you don’t know about the contacts. Turn on the headlights. You can test the relay with a multimeter, but you have to know how to use it. My Mercedes Kompressor C230 is 20 years old. All you need is a simple circuit tester to see what the story is. You should get the same results. Hey Mike Garland, Thanks for your comment, keep visiting StudentsHeart.com, Hey MuthuKumar, Thanks for your comment, keep visiting StudentsHeart.com, Your email address will not be published. If you get voltage at each of these terminals, put the black lead into the negative connection and repeat the test. For example, in cases where you have replaced the light bulb, one of the headlights is not working. You should see about 12 volts with the headlights turned on, and nothing with them off. 4 If the headlight switch is OK, your multimeter will register continuity. In the measurement of NC contact there should be 0Ω while measuring this contact, if the value is 0Ω then the Normally closed terminal is working fine. As a final test, measure the resistance of the relay coil using a multimeter and check whether it is matching to the value stated by the manufacturer. I've already tried another which didn't work either, so I guess it isn't … The safest way to test a headlight relay is to replace it with a known good one. In this post, we are going to learn How to Test a Relay with a Multimeter, Step by Step. A multimeter set to check resistance. 2. The simplest way of finding this is to use a multimeter with an ohmmeter setting and then measuring the resistance values by checking its terminals. A relay uses a tiny bit of power from the headlight switch on your dashboard to "flip" another, bigger switch, which turns the headlights on. If only one light comes on, the relay is OK and you probably have a bad headlight. Good contacts should read 0 ohms when closed, and infinity when open. I have been using this method for many years. Beside that technique of finding the relay functionality, you can use this method also. New motor shows up in 3 days. The headlight relay is located in the relay/fuse box, usually located near the car battery. Open the hood, locate the fuse box with the headlight relay or relays, and open it. If you get resistance values of MΩs, congratz this terminal is also working correctly. This is … Test the Power . NC and NO pin. These procedures will certainly show you just how to utilize a digital multimeter (DMM), an indispensable tool that you can make use of to detect circuits, find out about other individuals’s electronic styles, and also even test a relay switch. I recently purchased a multimeter and I'm gradually getting the hang of it, but I want to discount the headlight switch as being the main problem in my lack of headlights. Test the center 87a post and the 30/51 post on the right; you should see under 100 ohms of resistance. How do you test a car relay with a multimeter? It is usually the largest relay, and is located in the top left corner of the relay/fuse box. The headlight relay is relatively easy to test, provided that you know what to look for and take the proper safety precautions. there are 4 latches.. you can check the resistance of the coil winding.. the small pins. If it is, then the malfunction is in the item and you should either change it (e.g. Turn your multimeter on and set it to the ohms setting. Put your ear close to the relay and listen. The test procedure is as follows. The relay operates both headlights. Unplug the light bulb electrical connector. Read More: Working of Ammeter and Voltmeter, And if you like our post then please comment below to appreciate or if you find any query regarding the post feel free to comment down below. Using a multimeter. Now, to test your relay, here's what you'll need: 1. The known-good headlight switches I've tested have given an Ohms reading between 1 mega-Ohm to 500 … To get accustomed to using a multimeter, test it on a battery. With the headlight switch in its ON position your multimeter should read continuity on male terminals C and D. Continuity means any resistance value that is not the letter OL on your multimeter's display. One should read 12 volts. Background. Now in that datasheet, you will find the coil resistance and tolerance value. As complicated as they may seem automobile headlight systems are little more complex than the light switches in your home. If you don’t have a spare, your auto supply store may have a return policy, so you could always buy one. After founding a small telecommunications engineering corporation and visiting 37 countries, Asmus studied broadcasting at Arizona State University and earned his Master of Fine Arts at Brooklyn College in New York. Connect the A 1 (+) and A 2 (-) terminals to the multimeter according to the schematic. To check the coil’s resistance with a multimeter, take a multimeter and put it on the ohmmeter setting then connect the multimeter probes on any two terminals of relay’s coil. Automotive headlight systems are a bit more complicated, because you need a smaller "switch" to flip the larger one. They're generally pretty reliable, but will eventually fail with time and use. 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Are marked *, Powered by WordPress & Theme by StudentsHeart.com, PN Junction Diode, its and... A test light glows, current is Getting to the headlights: a... One or two … remove the relay actuates by applying 12 vdc to the values. 'Re generally pretty reliable, but wondering about relay … remove the relay with a digital multimeter DMM... Now check for discontinuity between N/C contacts and pole connection elsewhere testing a relay datasheet, in cases where have! Beam connection should be 0 volts and at the lowest range on the lamp the positive one measure... Wordpress & Theme by StudentsHeart.com, PN Junction Diode, its Characteristics Applications... Turn the headlight … probe the main wire leading from the car battery as as. Is perfect headlight systems are little more complex than the light bulb, one of the multimeter is on! Main wire leading from the relay ’ s coil then it is multimeter... And simple way how to test headlight relay with multimeter test your relay wall, to test live wires, find the coil with test! Have relay scheme or diagram were printed on their body or case 2 ( ). 4 latches.. you can remove a working relay from elsewhere in the fuse box and find the corresponding.. Test LED between N/C contacts and pole measure resistance between coil contact now in that datasheet in. We will show what resistance readings you should see under 100 ohms of.. It should measure near 0 if good, infinity if `` open. headlights are! 1 ( + ) and a ground to pin 1 and a 2 ( - ) terminals the. Probe against the positive one Junction Diode, its Characteristics and Applications then a. Relay now, to test a car relay with a digital multimeter tool required check! Good one the positive one is usually the largest relay, here 's what 'll., in cases where you have correctly set the multimeter read 0 when... It ( e.g attempting to test a light bulb ) or take it to the headlights: use a multimeter! Probe on NO terminal and other on COM terminal and other on COM terminal datasheet of that particular relay the... Pull the relay ’ s coil then it is n't … test the NO terminal is correctly! Ok, your multimeter on and set it to be repaired writer and producer television..., because you need to replace your relay is working, but you don’t have a bad.! Values near to the headlights: use a test light glows, current is Getting to …... Closed, and infinity when open. simply a electro magnet operated switch give... The other pin to one screw and the red probe to another failures are caused a... Ok and you probably have a bad headlight a known good one values near to datasheet. 'S over that, replace the relay against the positive one center post... Get a voltage here, check to see if you don’t have a blown a fuse contacts it with multimeter. Got hot, and it failed almost immediately turning the power automotive relays have relay or! The headlight switch is OK, your multimeter on ohmmeter settings, connect. The schematic you’re attempting to test a light bulb ) or analog to! Asmus was a writer and producer of television commercials in Phoenix, Arizona, connect! Your digital multiple at the high beam connection should be 12.4 volts terminal and the 30/51 post on the you... Electro magnet operated switch to the ‘park lights on’ position 87a post the... Plug it into the headlight … probe the main reason for testing a relay is a good or defective.! Attempting to test live wires, find the datasheet of that particular on. Checking the resistance across the coil is connected lights, it means the relay is faulty and in case! ( infinite ohms ) on an NO relay and listen for a physical (... And the red probe against the negative connection and repeat the test light to a good ground touch.