TOPDON · Service maintenance and measurement devices
Digital test pen for DC voltage, polarity, and limited circuit load testing in automotive wiring; 3.3–65 V measurement and 5–30 V load test.
Product information
The TOPDON CT100 is a digital automotive test pen that indicates voltage and polarity in fuses, sockets, and supply lines. It helps investigate weak connections with load testing. It does not read OBD fault codes; it is not for use on high-voltage electric vehicle batteries.
Vehicle and part coverage
A make-model software list, as found in diagnostic devices, does not apply to this product. Compatibility is determined by the part to be measured, the electrical system, the operating range, the probe or connection method, and the manufacturer's safety limits.
Product details
A non-functioning headlight, accessory, or lack of power at a socket does not necessarily mean the fault originates from the component itself. Fuses, wiring, connections, and ground paths can also cause the same symptom. This test device numerically displays the DC voltage at the point of contact.
Thus, you observe the measurement value instead of just whether the light turns on. The result on the screen is examined in conjunction with where you took the measurement and where the clamp is connected. A vehicle wiring diagram is necessary to find the correct test point.
The product does not connect to an electronic control unit via the OBD socket; it operates by contacting the electrical circuit with the probe and clamp.
Product details
Three basic pieces of information are gathered in the same handheld body: voltage value, polarity direction, and behavior under load in suitable circuits. Plus and minus signs with colored illumination are read along with the number on the screen. Red indicates positive, green indicates negative polarity. This display simplifies understanding the connection; it does not replace the vehicle's wiring diagram.
Numerical resolution and measurement accuracy are also different concepts. The screen displaying tenths of a volt does not mean zero measurement error under all conditions. Measuring only voltage in a sensitive sensor circuit is not the same operation as connecting a test load to the circuit.
Product details
The presence of voltage in a wire does not solely prove that the connection can carry sufficient current when the consumer is operating. An oxidized or loose connection may behave differently under load. The manufacturer describes using the load test by pressing the button for five seconds in a suitable circuit. The purpose of the test is to examine the behavior of the supply line under load.
Since the test current is a maximum of 1.2 A, do not consider the device a load test for high-current starter motors. Although the voltage measurement upper limit is 65 V, the load test upper limit is restricted to 30 V. The two limits are not transferable; this distinction is particularly important in 36 V systems.
Product details
The coiled test cable facilitates reaching sockets distant from the connection point. In tight spaces, you can bring the device body close to the socket and see the measurement value directly. The interchangeable probe design reduces the necessity of continuing work with a damaged or unsuitable tip.
Care must be taken not to touch the metal tips of the probe to adjacent pins, and not to damage socket seals and terminal structures. Instead of randomly piercing wire insulation to access a terminal, use the vehicle manufacturer's measurement method. The quality of contact between the clamp and probe affects the interpretation of the measurement; fluctuations due to loose contact are not considered direct component failure.
Product details
If a vehicle outlet or light is not working, first determine under what conditions that circuit is energized. Some circuits are only powered when the ignition is on. By measuring at the test points indicated on the diagram, you can compare the status of the fuse's input and output sides.
The presence of voltage on one side and its absence on the other, or its absence on both sides, requires different investigation steps. The obtained number does not indicate the fuse's amperage rating or the health of the entire circuit. After measurement, examine the physical connections and the relevant consumer separately.
The pen's contribution is to convert the presence of power into a visually observable value.
Product details
A connected consumer may not work even if voltage is read at a power socket. In this case, measuring the connection at idle may not be sufficient. If the vehicle service procedure allows for load testing, the behavior of the line can be examined with the CT100 within the specified voltage and current limits. Compare the result with a known good connection and the same operating conditions.
If the change appears only on one side of the socket, the wire end and terminal connection can be investigated. However, applying a test load to the output of an electronic control module is not appropriate for every circuit. Do not test control unit outputs, communication lines, or sensor signals as if they were ordinary power supplies.
Product details
Wire colors on a disconnected accessory may have changed over time, or a different wire may have been used in a previous repair. Instead of relying on wire color, use the diagram and measurement together. The digital display indicates positive or negative polarity relative to the reference to which the clamp is connected. The meaning of the result may also change if the reference connection at the same point is changed.
First, select a reliable reference point; then, touch the probe only to the terminal being inspected. The colored display makes it easier to distinguish polarity in poorly lit areas. This usage does not additionally determine the current the wire can carry or the suitability of the accessory to be connected.
Product details
The manufacturer defines this model for automotive DC circuits. Mains AC measurement, high-voltage batteries of electric vehicles, and insulation resistance testing are not within the scope of this device's described functions. The term 12 V, 24 V, or 36 V vehicle does not mean that every connection on the vehicle can be tested.
The manufacturer's procedure is followed, especially for airbag firing circuits and sensitive electronic lines. A pulse shape requiring an oscilloscope, a communication line, or a diagnostic of an intermittent signal cannot be resolved solely by the voltage count on the screen. A change observed during measurement is a finding; it is not a result that solely identifies the faulty part.
Product details
A simple test light indicates the presence of voltage with light. This digital model combines a numerical voltage and polarity indicator with load testing in suitable circuits. When selecting a multifunctional multimeter, consider other required measurement types such as resistance, continuity, or current; these features are not implicitly assumed here.
An OBD device like the TopScan Master performs a different function by reading codes and data recorded by vehicle modules. In case of a power supply fault, OBD scanning and physical electrical measurement can complement each other. Purchasing a test pen solely to clear the engine warning light is not an appropriate choice for the task.
Product details
The package in the European product listing consists of the CT100 test device, a 2 mm probe, an alligator clip, an adapter, a carrying case, and a quick start guide. The manufacturer states that the device does not require separate batteries. This does not mean the measured circuit is safe or can be used at all voltages.
Before each use, check the cable, clamp, and probe for damage. After testing, store it in its case, protecting the tip. Do not let the cable contact hot engine parts or moving mechanisms. Usage conditions and warnings on the product take precedence over general automotive advice.
Related pages
Technical Resources
Technical information verified with official sources on October 26, 2026.
FAQ
No. It performs DC voltage, polarity, and load tests on suitable circuits in vehicle electrical systems. A separate supported OBD fault detection device is required to access the fault memory of engine, ABS, or airbag control units.
These are two separate operating limits. The voltage indicator measures the 3.3–65 V DC range. The test applying load to the circuit is limited to 5–30 V. Being able to read voltage in a 36 V system does not mean a load test can be performed at the same point.
The product description does not define it as an SOH or CCA battery analyzer. Voltage and limited load testing aid electrical investigation. A dedicated battery tester is used for capacity assessment according to battery type and standard.
No. The specified measurement range is for DC. Do not consider this range or automotive use sufficient for mains AC voltage. Mains electrical measurement requires separate, appropriate class equipment and expertise.
TOPDON specifies operation without requiring separate batteries. However, minimum measurement voltage and correct reference connection are important. Do not automatically assume that the absence of display means no energy is present in the measured circuit.
The approximately 3.8-meter cable facilitates access to test points distant from the fixed reference connection. Cable length does not increase the measurement range or load test limit. The cable must be kept away from hot engine parts and moving mechanisms in the engine bay.
Comparison
Compare products in the same class with information on usage level, service tasks, and price.
| Model | Level | Usage | Price | View |
|---|---|---|---|---|
| TOPDON CT100TOPDON | Service |
| ≈ $1195,921.76 TL charged · VAT included · import duties excluded | View |
| TOPDON V3000TOPDON | Service |
| ≈ $27913,883.79 TL charged · VAT included · import duties excluded | View |
| ANCEL BST600 12V/24V Battery Tester with PrinterAncel | Service |
| ≈ $1718,490 TL charged · VAT included · import duties excluded | View |
| Autel MaxiBAS BT609Autel | Professional |
| ≈ $68133,900 TL charged · VAT included · import duties excluded | View |
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