How to Test a Relay Switch

Where there is an electrical device or an electric vehicle, there is one thing which will be thereby default. It is similar to a miniature circuit breaker and does almost the same work. These are called relay switches. Just like spark plugs and ignition coils in vehicles, these are an important part of a vehicle, to be specific. These are important to regulate the electrical overloads in the car's electrical system and open when triggered by an electronic signal. Now if these are not working properly, you can imagine what the car or any electronic device will go through. The need to test these relay switches is justified then, isn't it? Why not check out how to test a relay switch?

Modus Operandi of a Relay Switch

A fuel pump relay switch or a relay is basically a switch which is operated electrically. These need an electrical signal to be activated as mentioned previously. What a relay does after it gets activated is that it connects an electrical supply to a particular accessory. In the case of a car, it is the fuel pump. There are two parts of a relay, the first part utilizes an electromagnet and then there is the secondary electrical circuit inside. Now the primary half of the relay closes the secondary half of the relay. It is powered in a manner akin to a light bulb circuit. Typically when testing the relay switch, the relay contacts, operation and activation circuits are tested.

Testing a Relay Switch

For testing a relay switch what you need is high-impedance test light, Ohmmeter and 2 jumper wires. Considering that you have got hold of the relay switch which is acting funny (read not working properly), here is the actual process.

Relay #1
If required, turn the ignition on to energize the specific circuit you intend to test. What you have to do next is get the connection of the alligator clip from the testing light with a good ground on your vehicle.

Relay #2
Now probe the wire which will be jutting out of the relay switch, which is reaching the component. Do this with the help of the tip of test light. One indication that the car relay is working properly is that the bulb of the test light will glow. That also means that there is proper voltage.

Relay #3
The wires feeding voltage to the relay have to be checked next in the same way as mentioned earlier, with the help of a test light. There is voltage if the light glows and if that does not happen, consider zero voltage there. In that case the voltage source may have to be checked.

Relay #4
Power and control terminals of the relay switch have to be identified next. After that see if the two power terminals are connected with the help of an ohmmeter. If there is a continuity between the two, it is a sure fire signal that it is a bad fuel pump relay, and the relay needs to be replaced.

Relay #5
In the next step you have to connect a jumper wire, which should be between the positive terminal of the battery and one of the control circuit terminals on the relay. Using another jumper wire, connect the other control terminal to the ground. Ideally, you should have a 'click', on making the second connection. If that does not happen try interchanging the connections. If even after reversing the connections you don't get that click, replace the relay.

Now, you are almost done here! As the finishing stroke, connect the jumper wires akin to the connections earlier. Use an ohmmeter to check for continuity between the two terminals. In this case, if there is continuity, consider the relay to be in good shape. If it does not happen, then replace the relay.

Hopefully, you will have preserved the vehicle manual, in case you need to see color codes for identifying power and control circuit wires on any relay and knowing how to wire a relay in the first place. If you feel this is too much of a hassle, the best way would be to consult a mechanic and see how to test a relay switch! This is where I sign off.