The CarRundown verdict.
We recommend the Topdon CT100 for anyone who wants a fast first answer to an electrical problem. It identifies polarity, runs load tests and gives clear audible and visual alerts, with a long oil-resistant cable and an interchangeable probe and clip that work on cars, trucks, RVs and EVs.
Many electrical faults come down to whether a circuit has power, ground and a healthy load. The CT100 is a hand-held circuit tester that answers those questions quickly, with an LCD and alerts.
The details that matter.
| Exact variant | CT100 · Default Title · SKU CT100 |
|---|---|
| Functions | Polarity identification, load testing, audible and visual alerts |
| Cable and tips | Long oil-resistant cable; interchangeable probe and clip |
| Vehicles | Cars, trucks, RVs and EVs |
| Listed price | $49.99 USD on Topdon's US store |
What stands out
- Polarity identification and load testing in one tool
- Clear audible and visual alerts
- Long, oil-resistant cable with interchangeable probe and clip
- Works across cars, trucks, RVs and EVs, per Topdon
Before you buy
- A circuit tester checks circuits, not battery health; a battery tester answers a different question
- Follow the manual and safety instructions for any live electrical work
- Topdon’s listing gives no voltage-range table in its text
A fast first answer
The CT100 identifies polarity and runs load tests so you can tell whether a circuit is live and carrying current before you start pulling parts.
Alerts you can notice
Audible and visual indications take the guesswork out of readings when your hands are busy under a dash or hood.
Built for the garage
A long oil-resistant cable and an interchangeable probe and clip make it practical around engine bays and trailers.
Where it fits
Add it to a basic tool kit alongside a jump starter and a scan tool. Our car emergency kit guide covers the rest of the roadside basics.
A good fit for
DIY owners and RV or trailer users who want a simple circuit and load tester.
Consider another option if
You want to test battery health or cold-cranking performance, which needs a battery tester.
Keep reading: Build a useful car emergency kit.
Your questions, answered.
What does the CT100 test?
Polarity and load, with audible and visual alerts, per Topdon.
Does it work on EVs?
Topdon lists cars, trucks, RVs and EVs.
Is it a battery tester?
No. It is a circuit tester; a battery tester checks battery health.
Product specifications checked against Topdon’s official product information on October 25, 2026. Recommendations are our editorial assessment. Our editorial standards.