CT100

CT100

Regular price $49.99
Regular price Sale price $49.99
Sale Sold out
Save 10% - Code TOPDAD

CT100

CT100

Regular price $49.99
Regular price Sale price $49.99
Sale Sold out

Auto Circuit Tester w/ Load Test, LCD, Polarity Alerts

The CT100 is a professional automotive circuit tester built for speed, accuracy, and everyday reliability. It helps diagnose electrical issues quickly, identifies polarity, runs load tests, and provides clear audible and visual alerts to take the guesswork out of repairs.

Built rugged with a long oil-resistant cable and interchangeable probe and clip, it works on cars, trucks, RVs, and EVs. No complicated setup—just fast, precise results for pros and DIYers alike.

  • Have questions? Ask an expert
View full details
4.8
Skip to product information

Features

  • Professional Load Test
  • Precision Voltage Testing
  • Polarity Protection & Anti-Reverse
  • Safe, Battery-Free Operation
  • Intuitive Status Light Indicators
  • Easy Operation & Extended Test Lead
  • Wide Vehicle Compatibility
Learn More

Warranty & Updates

  • 1 Year Warranty
  • WARNING: Cancer and Reproductive Harm For more information go to www.P65Warnings.ca.gov
Professional Load Test

Unlike basic test lights, the CT100 features a professional load test function (DC 5–30V, 1.2A Max). Hold the button for 5 seconds to check battery and circuit load capacity, quickly identifying aging batteries, weak connections, and voltage drops for faster, more accurate repairs.

Precision Voltage Testing

Equipped with a clear backlit digital display, the CT100 measures DC voltage from 3.3–65V with 0.1V resolution (±0.1V accuracy from 3.3–60V; ±0.2V from 60–65V). With a wider range than standard testers, it delivers dependable performance for both professional technicians and serious DIY users.

Polarity Protection & Anti-Reverse

Dual-color backlighting (red for positive, green for negative) and on-screen ± indicators activate instantly when the probe contacts a circuit. This intuitive feedback helps prevent reverse connections and protects sensitive vehicle electronics during testing.

Safe, Battery-Free Operation

Battery-free operation eliminates maintenance and downtime while improving safety during testing. Integrated protections include overvoltage alerts, overheating warnings, and component status monitoring for dependable performance in daily automotive diagnostic work.

Intuitive Status Light Indicators

Color-coded backlight indicators confirm polarity instantly, while additional alerts display overvoltage (“H”), overheating (“Hot”), and lamp abnormality (“ER1”) status—keeping key operating conditions visible at a glance during testing.

Easy Operation & Extended Test Lead

The 12.5-foot extra-long test cable improves access to hard-to-reach areas without repositioning the tester. Universal 4mm banana jack connections support interchangeable probes and clips, enabling flexible testing across cars, trucks, RVs, and other vehicles.

Wide Vehicle Compatibility

With a 3.3–65V testing range, this versatile tester supports 12V, 24V, and 36V vehicle systems, making it ideal for cars, trucks, RVs, commercial vehicles, and more. Perfect for checking fuses, verifying connector voltage, testing circuit integrity, tracing wiring issues, and diagnosing starting-related electrical faults.

CT100 Circuit Tester
2mm Probe
Alligator Clip
Adapter
Carrying Bag
Quick User Guide
4.8
Rated 4.8 out of 5 stars
Based on 6 reviews
Total 5 star reviews: 5 Total 4 star reviews: 1 Total 3 star reviews: 0 Total 2 star reviews: 0 Total 1 star reviews: 0
100%would recommend this product
Rating
Ratings
6 reviews
  • Joseph F.
    Verified Buyer
    1 week ago
    Rated 5 out of 5 stars
    Buy this tool!!!

    Great tool for quick electrical diagnosis.

    A must have for the toolbox

  • Robert K.
    Verified Buyer
    1 week ago
    Rated 5 out of 5 stars
    Great circuit tester

    This is an awesome circuit tester. I have several other test lights but this one has quickly become my favorite. The 4mm banana plugs give this an advantage over other circuit tester’s by allowing you more connection options. The load button is also a nice touch so the circuit can be verified for good connections. Topdon did a great job as usual. Thank you

  • Ron H.
    Verified Buyer
    22 hours ago
    Rated 5 out of 5 stars
    Works good

    Very nice product. You can add whatever leads you want thanks to standard banana plugs. The readout is spot on in accuracy. The load test works pretty slick. I haven't really used it, but from what I see it will be a nice tool at a great price.

  • Ronald Y.
    Verified Buyer
    6 days ago
    Rated 5 out of 5 stars
    Circuit tester

    It is convenient one small tool and you can test power ground 5 volt reference load test the circuit. I work on transit buses we have 12 & 24 volt system on the buses it really is an awesome tool. Once again Topdon you have made a great tool.

  • William B.
    Verified Buyer
    1 week ago
    Rated 5 out of 5 stars
    Awesome

    Outstanding transaction.