How to Test a Relay with a Multimeter?

Relays are the most common cause of problems with vehicles. They can be found in many different places and often serve one specific purpose, but when they go wrong it’s hard to pinpoint exactly what has caused them so much frustration for both owner’s as well mechanics.

When your car has a bad relay, it can cause many different problems. For example:

A common issue with electrical components such as relays is that they sometimes go out and need to be replaced or fixed so you don’t damage anything else in the vehicle when doing this work! Luckily for us amateurs looking at taking care of our own cars here today – testing out what kind might need servicing- there are simple tests we should know how to conduct.

What is a Relay?

When we apply a low voltage (and current) signal across the coil of our Relay, it becomes an electromagnet and pulls back against its own armature. As soon as this happens there are two possible outcomes: if you remove all power from within erratically switching device by removing cables or other connections then things will go back to how they were before; however–in more severe cases where people have tried pulling hard on various components inside their homes after misusing tools such type might break apart due mommy issues.

When the electromagnet is inactive, there are two contacts on each side: Normally Open (NO) and NC. When they come into contact with one another these make up what we call COM -short for “common point”. This means that everything else built-in to this system will share its power through this single point which leads back down to how electricity works in general.

The three terminals i.e., COM, NO and NC are all independent of each other with the exception that when a circuit is completed through them based on energization from either side – negative or positive terminal respectively- then whichever one was not originally hit will now act as ‘com’.

Where are Relays used?

Understanding the physical and mechanical aspects of a relay is good, but it won’t do much good if you don’t know how or where to use them. Imagine your car’s headlights: during evening hours (and sometimes at night), when traffic becomes scarce on roads around meadows while everyone heads home after work—I flick or twist near my steering wheel so that light from these vehicles can shine brightly into dark alleys between buildings structures waiting patiently until their turn comes back again tomorrow morning…

The headlights of your car are high-power devices that draw anywhere between 55W to 100W or more power. To ensure safe operation, the computer within each vehicle must be able control low voltage and low amperage motors directly without connecting them into any other component which could cause damage due its own requirements being too great for such small supplies available on most cars today.

The reason why we need relays in this situation is because they can handle bigger currents than normal switches while still remaining circuit protective against overloads by shutting off individual circuits when becoming overheated.

When the car’s computer energizes its coils and we connect them to NO terminal, then this allows for easy control of headlights without burning or damaging anything. This is exactly what happens in an actual vehicle with their lights turned on – they’re pulled by hackers through remote switches.

When we turn on the headlights switch in our car, it’s computer reads this signal and activates coils of relays. One type of relay has an armature that switches its position which then turns your lights On or Off as desired! When you decide to go without any electricity for fuel efficiency purposes by turning off their power at source (headlights), there is no need to worry because using natural methods like these will never harm anything.

Relay Safety:

The process of relay testing is simple, but it’s important to be safe. It helps if you take these things into account when working with relays:

  • You can’t just go searching for a relay in your car and expect it to be the right one. The wrong type of these controls could cause short circuits or power surges that will damage electrical systems, so make sure you’re getting an authentic part from an actual manufacturer.
  • Handle the relay with care and don’t drop it. If you find that there is internal damage, unmodified relays can cause burning or melting of wiring – so be careful not to modify your own.
  • Working with relays and anything involving electricity in a space that contains flammable or explosive gasses such as gasoline should be avoided.
  • The wiring system in your car is often a mystery to those who are not technically savvy. The service manual will help identify and understand what relays or other devices need servicing, but it’s important that you learn as much about this topic before taking on any repairs.

How to Test a Relay?

  1. You can find the relay that controls your dash lights and other features in two different locations, under or inside of your vehicle. If not sure which one it is then consult an instruction manual for assistance.
  2. The easiest way to test your relay is by switching it out with a known good replacement. The disadvantage, though not as bad as cooking first units, could be cooking second ones and also costs money. You should inspect the connectors while you’re taking them apart so they don’t get dirty or contaminated before installing into place again but that’s about all there really isn’t any need for complicated procedures here since testing just requires putting two components together in most cases – who doesn’t love shortcuts?
  3. Grab your multimeter and set it to measure resistance. Touch the leads across both sides of an electromagnet coil pin, then count how many ohms there are in that circuit – anywhere from 50-120 will do! If one side or either end has open circuits (less than 0), replace that winding with another new relay for proper operation once again.
  4. When you’re measuring the resistance of a switch, it’s important to know whether or not there are any other elements in between. For this reason we will be using both an ohm meter and continuity vampire test tool as well. The first step is to leave your multimeter on ‘ohms’ mode while touching each lead across each pin from left-to right… A normally open relay should read OL (Open).
  5. The relay should make an audible “click” as the electromagnet coil energizes and closes the switch. Polarity doesn’t matter on this 4-pin, but it is vital for diode relays.
  6. With the battery still energized, jump from one switch terminal to another and connect a test light between them. The current should flow through these junctions without hesitation or delay as soon as you put it there; if not then try again by repeating these steps until success is achieved.
  7. To test the relay’s voltage at the switch, remove the cover and set the multimeter to DC volts. Touch leads across pins or connectors on test light if it has one so that you can get an idea of what each lead represents (e-g red/black). The reading should match up with battery voltage.
  8. Check your wiring to make sure you have the right resistance. Disconnect both ends of an electrical wire and measure how much current flows through it with a meter, then compare that number against what would be expected if all connections were perfect—that’s usually around 0 or low voltage (going higher means worse). If there is too much flow for either situation but particularly one where nothing else seems wrong-then chances are good something may indeed need fixing.


The beginner’s guide to relays, what they are and how they function. A simple explanation for those who don’t know much about them or just need a refresher. This article also covers where you can find some useful information on testing out your own repairs with multimeters – something that could come in handy down the road if there are any issues with other parts of our vehicle (and trust us; things will break).