1 / 7

Product guide

TopDiag P100 Automotive Circuit Tester

The TopDiag P100 automotive circuit tester combines DC and AC voltage, resistance, and tone modes for diagnosing vehicle electrical circuits. Its claimed 40-foot total cable reach is intended to help access wiring farther from the vehicle battery, though customer feedback is mixed on cable quality and durability.

At a glance

Four modes cover DC voltage, AC voltage, resistance, and tone-based circuit checks.
The listing describes component activation for vehicle electrical parts such as motors, lights, and fans.
Short-circuit protection is claimed, with an internal circuit breaker that trips if overloaded.
A built-in flashlight is described for use in dim work areas.

Price

$46.74Save 15%

Reference price: ~~$54.99~~

Price checked: Nov 14, 2026

View offer

Pros and cons

Pros

The listed modes give buyers more than a basic test light, including AC voltage and resistance readings.
The claimed 40-foot cable reach may help with troubleshooting wiring toward the rear of a truck or trailer.
The listing describes component activation as an aid to checking individual electrical parts.

Cons

Customer feedback includes reports of the tester breaking after limited use, so durability is a reported concern.
Cable quality receives mixed customer feedback.

Technical specifications

8 specifications

Identity
Brand	TopDiag
Model	P100

Power and battery
Power configuration	Battery Powered

Dimensions and installation
Dimensions listed	6 x 2.4 x 1.2 inches
Weight listed	1.9 pounds

Testing and compatibility
Working modes	DC Voltage, AC Voltage, Resistance, Tone On/ Off
Voltage input range	9V to 70V
Supported vehicle types	Vehicles (12V cars, 24V trucks, trailers) and their electrical components

What to know before buying

Listing details to confirm

Cable length is inconsistent across the listing: the title claims 40 feet, while feature text describes a 20-foot tester cable plus a 20-foot extension. Confirm the exact cable arrangement for the selected listing.

What’s in the box

Included

1 P100 tester

Who is it for?

A good fit for

DIY vehicle owners tracing electrical faults in 12V cars or 24V trucks.
Technicians and enthusiasts who want voltage, resistance, tone, and component-activation functions in one probe-style tester.
Buyers who need to reach wiring along a trailer or toward the rear of a vehicle.

Less suited to

Buyers who need a tool with consistently dependable durability, given the reported breakage concerns.
Anyone seeking a general-purpose household electrical tester rather than a vehicle circuit tester.

TopDiag P100 Automotive Circuit Tester · photo 2 — Additional product photo 2

Customer reviews on Amazon

4.6 / 5 · 680 ratings

5 stars77%77%
4 stars14%14%
3 stars3%3%
2 stars1%1%
1 star5%5%

Customer feedback describes the tester as easy to use and useful, with positive comments about quality and value and mention of its AC and DC options. Durability and cable quality are less consistent, including reports of failure after two uses. For buyers using its listed voltage and resistance modes on vehicle wiring, those concerns matter when weighing a multi-mode feature set against expected long-term reliability.

Positive themes

Customers describe it as easy to use and appreciate its functionality and value.

Negative themes

Some customer reports describe the tester breaking after two uses.

Mixed feedback

Cable quality receives mixed feedback, and durability comments are not uniformly positive.

Frequently asked questions

What kinds of tests does the TopDiag P100 list?

The listing names DC voltage, AC voltage, resistance, and tone on/off modes. It also describes component activation for vehicle electrical parts.

What vehicles is it listed for?

The compatibility details name 12V cars, 24V trucks, trailers, and their electrical components.

How long is the cable?

The title claims a 40-foot cable, while the feature description specifies a 20-foot cable plus a 20-foot extension. Check the selected listing for the cable arrangement.

Does the listing describe overload protection?

Yes. It claims short-circuit protection and says an internal circuit breaker trips if overloaded. This is a listing claim, not an independently verified performance result.