An automotive test light or circuit tester can check the presence or absence of electricity between two locations in a vehicle.
This tool is used to test load carrying electrical circuits. A 12 volt test light is a handy visual indicator that voltage is available, but can’t measure current flow higher than the test light’s own current consumption.
Test lights for cars are composed of a handle similar to a screwdriver except that the handle is hollow with a flexible wire passing through a removable rear cap that provides a contact on the inside of the cap.
Typically, there will be a spring between the bulb and the inside end of the probe, which extends like a screwdriver bit out of the handle except that it has a sharp tip.
Using the tool involves clipping the wire onto a metal component like your vehicle’s chassis or your battery’s negative terminal and then using the probe to check if any electricity passes through the probe into the wire or vice versa.
If there’s electricity, then a light on the probe will illuminate. In this article, we’ll discuss how to use a test light on a car.
What is a test light?
A test light, or test lamp, is a simple piece of electronic equipment used to test the presence of electricity in a circuit. Typically, it is used to check the voltage on a circuit, like on a wire or on a fuse, but it can also be used to check grounds.
A test light mainly consists of a light bulb, usually an incandescent lamp (bulb) or LED bulb, a probing end, and a clamp.
When testing for voltage on a circuit, the clamp is connected to a known good ground, like the negative side of the battery. When the probe side of the test light touches voltage, like the positive side of the battery, the bulb will light.
Understanding the Basics
Before we dive into using the test light, let’s understand the fundamentals of electricity in your car.
- Positive wire: This wire carries electrical current from the battery to the various components in your car, like lights, sensors, and the starter motor. Think of it as the “supply line” for electricity.
- Ground wire: This wire provides a return path for the electrical current back to the battery. It completes the circuit, allowing electricity to flow.
A test light works by completing this circuit. When the test light’s probe touches a live positive wire, the circuit is closed, and the bulb lights up, indicating the presence of electricity.
What does a test light do?
A test light is an electrical test instrument used to test for electricity in a circuit. When electricity is found, the test light will illuminate.
To test for voltage on a circuit, you would first have to connect the test light’s clamp to a known ground source, this is usually the negative battery terminal.
After that, you will use the probe end of the test light to test the contacts of fuses in the car’s fuse box panel or pierce a wire. When the test light illuminates, this means there is voltage on that circuit.
The opposite can be done to test for a good ground. The clamp of the test light will be connected to the positive battery terminal and the probe end will be used to find a ground.
Internal Structure of Test Lights
If you know how test lights are built, it will help you enhance your safety, help with troubleshooting, and allow you to make informed purchase decisions.
At the same time, understanding the internal components and their functions ensures you use the tool correctly and avoid accidents.
The Components
Test lights may appear simple on the outside, but their internal structure is carefully designed to ensure accuracy, safety, and durability. Here are the key components that make up a standard test light:
Test Probe
The probe is a slender, metal rod that users touch to the circuit component being tested. It is usually made of highly conductive materials like stainless steel or brass, ensuring efficient transmission of electricity.
The probe’s tip is pointed to allow easy access to small or recessed contact points.
Indicator Light
The heart of the test light is the indicator, normally a neon bulb or LED. When the probe detects voltage, the bulb lights up, providing a clear visual signal.
Neon bulbs are common in basic test lights because they glow brightly at a wide range of voltages and have a long lifespan. LEDs are used in more advanced models for their energy efficiency and brightness.
Housing
The housing encases all the internal components, protecting them from damage and ensuring user safety. It’s often made from durable, insulating materials like high-impact plastic or composite.
The housing is ergonomically designed to provide a comfortable grip. It is often transparent or translucent near the indicator light to allow visibility.
Wiring
Inside the housing, the probe is connected to the indicator light through insulated wires. These wires are designed to handle high voltages and are securely soldered to prevent loose connections. The insulation is highly required to protect against electrical shocks and short circuits.
Ground Clip
The ground clip, usually attached to a flexible wire, is clamped to a known ground point in the circuit. This clip completes the circuit, allowing the current to flow through the test light and illuminate the indicator if voltage is present.
The wire connecting the ground clip is designed to be flexible and durable. This is often covered in rubber or silicone to withstand wear & tear.
Internal Resistors
Resistors are incorporated to limit the amount of current flowing through the test light. This prevents the device from drawing too much power from the circuit, protecting both the test light and the circuit being tested.
The resistors are carefully chosen to match the specifications of the test light. As a result, test lights can guarantee accurate readings without overloading the circuit.
How Many Types of Test Light Are There?
The first step to mastering the use of a test light is to understand the types of test lights. There is a range of test lights out there, so knowing their functions lets you choose the best automotive test light for the task at hand.
Some are designed for only basic functions, while others are used for a range of electrical functions. Here are some of the test flights that are out there.
#1. Non-Contact Voltage Testers.
This kind of tester allows you to test for voltage without coming in contact with your car’s electrical components. It is battery-powered and quite easy to use.
#2. Neon Voltage Testers.
This test light is designed to detect the presence of voltage alone. It also requires contact with the components, so you’d need to be careful when using it. It is a good substitute for the no-contact test light.
#3. Plug-In Circuit Testers.
This tool has three neon lights that light up in different patterns, each of which specifies a particular test outcome. You can easily interpret what the light patterns mean.
#4. Continuity Tester.
This test light is battery-powered and is great for diagnosing a range of electrical faults. It also comes with an LED digital display that relays information to you.
#5. Multimeter
Test light vs. multimeter? Both tools detect voltage. It is just that the multimeter is used to perform a range of functions.
It is built with a dial for fixing the test function, and when used correctly, the multimeter can offer a range of information on different car components. So you may not need too many test lights when you have a multimeter.
#6. Solenoid Voltage Tester.
This is another test light that is designed to execute a range of testing functions. It is not battery-powered and is also inexpensive. It indicates the presence and amount of voltage by either increasing or decreasing its clicking or vibrating.
#7. Digital Clamp Meter.
This tool can function as a multimeter and a current sensor. Although it is a bit pricey, this test light is easy to operate and safe to use.
Why Do You Need to Use a Test Light on Wires?
#1. Quicker Diagnose.
The main reason to use a test light on wires is to quickly diagnose electrical issues in the wiring of any system. By illuminating the wire with a low-voltage current, you can determine whether or not there is power being sent through it.
Test lights are great for diagnosing shorts and open circuits in automotive wiring systems, residential wiring, commercial applications, and more.
#2. Easy to Use.
Test lights are very easy to use and require no special skills or knowledge to operate properly. All you need is a basic understanding of how electricity works and the ability to follow simple instructions.
With just a few clicks, you can easily check for current in your wires and determine if there is an issue with the wiring.
#3. Safe to Use.
Test lights are a safe way to check for electricity in wires because they use low-voltage currents. This means that there is no risk of electrocution when using the device, making it much safer than other methods of checking electrical wires.
The Benefits of Using Test Light on Wires
#1. Portable.
Test lights are small and lightweight, making them highly portable. This makes them great for testing wires in hard-to-reach places or narrow spaces where a standard multimeter may not fit.
Test lights can easily be stored in toolboxes, glove compartments, or even pockets so that they’re always there when you need them.
#2. Quick Results.
Test lights provide quick and easy results, making it easier to identify electrical issues quickly without having to do any calculations. This is great for DIYers or electricians who are trying to diagnose and resolve wiring problems quickly and efficiently.
#3. Cost-Effective.
Test lights are relatively inexpensive compared to other types of electronic diagnostic tools. This makes them a great option for those who are looking to save money while still getting the job done right.
How To Use A Test Light
If you know your way around a test light, you’ll be able to tell when critical electrical parts have failed. Various situations call for the employment of test lights, and we’ll go over those below.
Positive Voltage Test
Verifying the functionality of the test light should be the initial objective. To do this, you’ll need to secure the test light to a stable ground. Here, the ground source is the exposed metal of the vehicle’s frame.
Another option would be to use the negative terminal of the battery. To find a positive voltage source, such as a fuse or the positive terminal of the vehicle battery, gently touch it with the probe. Everything is OK to go if the test light comes on.
Using Test Light On Fuses
Using a test light, you may check to see which fuses in your vehicle are active. Please follow these procedures.
Navigate to the panel housing your vehicle’s fuse box. To accomplish this, you may need to consult the owner’s handbook. After that, take off the cover to see where the fuses are located.
First things first: turn off the engine. The next step is to secure the test light’s clip to a non-painted metal surface, such as a bolt, in order to provide a good ground.
As an additional excellent alternative, you might use the negative terminal of the battery. Where the panel housing the car’s fuse box is located determines everything.
Checking for Short to Ground with Test Light
Perhaps you’ve noticed that your vehicle’s power is starting to dwindle. When troubleshooting other parts of its functionality fails, the next step is to inspect the electrical system.
The point is to make sure the electrical resistance is correct; checking the ground circuit of your vehicle is the easiest approach to achieve this. This is the way to do it.
Make sure the positive circuit works. You can proceed to check the ground circuit if this is determined. This can be accomplished by attaching the positive end of the test light—ideally a circuit tester—to one end of the device.
After that, you need to make sure that the other end of the tester is touching the component’s ground wire. If the test light comes on, it means the ground circuit is good; if it doesn’t, you may have to look elsewhere for the source of the higher resistance.
FAQs.
Q: Is it safe to use a test light on live (positive) wires?
Using a test light on live wires can be safe when done correctly. However, it’s essential to exercise caution and follow safety precautions.
Ensure that you have a good ground connection, wear appropriate safety gear, and avoid touching the metal parts of the probe when testing live wires.
Q: How can a test light help in diagnosing ground wire problems?
When using a test light on ground wires, it helps identify if a ground wire is properly connected or if there’s a break in the ground circuit. If the test light doesn’t illuminate when connected to a ground wire, it suggests a grounding issue that needs to be addressed.
Q: Can using a test light damage electrical components or wires?
When used correctly, a test light should not damage electrical components or wires. However, if the test light is used improperly, such as connecting it to a high-voltage source or accidentally shorting wires, it can potentially cause damage. Always exercise care and follow proper procedures.
Q: Can a test light be used to check the continuity of a wire?
A test light is not typically used to check continuity (whether a wire is unbroken). Instead, a multimeter or continuity tester is more suitable for that purpose. These tools can determine if a wire has a continuous path or if it is broken or disconnected at any point.
Q: Can a test light help find parasitic battery drain issues in a vehicle?
A test light can be used to identify parasitic battery drain issues in a vehicle. By disconnecting the negative battery terminal and placing the test light in series between the disconnected cable and the battery post, you can check if there is an abnormal current draw.
If the test light illuminates brightly, it indicates excessive current draw, which can help pinpoint the source of the drain.
Q: Are there any precautions to take when using a test light in a car’s electrical system?
When using a test light in a car’s electrical system, it’s crucial to disconnect the battery’s negative terminal before testing.
This prevents accidental short circuits and ensures safety. Additionally, be cautious when probing wires to avoid damaging delicate electrical components or causing unintended shorts.
Final Words
Test lights are great tools to have in your tool kit. Indeed, knowing how to use a test light is a skill that everyone who owns or uses a vehicle must have. This is because it allows you to ascertain the car’s electrical system and its components easily.
This way, you know when the problem is not from the electrical system. So next time your car develops a fault, you should be able to use your test light to eliminate some of the improbable causes of the car’s problems.