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🛠️ Stretch your reach, not your patience — test smarter with OTC 3642!
The OTC 3642 Truck Electrical Circuit Tester is a professional-grade diagnostic tool designed for 12V to 24V truck systems. Featuring a 7-inch stainless steel probe and an extra-long 24-foot coiled cord, it offers unmatched reach and precision. Its oversized clamp ensures secure grounding on larger components, making it an essential tool for technicians seeking reliable, efficient circuit testing.





| ASIN | B005J3KR92 |
| Best Sellers Rank | #310,572 in Tools & Home Improvement ( See Top 100 in Tools & Home Improvement ) #390 in Circuit Testers |
| Brand Name | OTC |
| Color | Red |
| Customer Reviews | 4.6 4.6 out of 5 stars (187) |
| Global Trade Identification Number | 00731413505805 |
| Included Components | 12V–24V Truck Circuit Tester |
| Item Dimensions | 13.9 x 2.1 x 0.1 inches |
| Item Weight | 1 Grams |
| Manufacturer | OTC |
| Measurement Type | Voltmeter |
| Minimum Operating Voltage | 12 Volts |
| Model | 3642 |
| Power Source | Battery Powered |
| Style Name | Modern |
| UPC | 731413505805 071090090493 012302669731 031112405643 971474694401 666661072208 012303704974 523161182243 |
| Unit Count | 1.0 Count |
| Warranty Description | 90 day Limited Warranty |
D**.
Quality test light
Great way to add a light load so your multi meter will read loaded voltage and not lie to you. Longer wire is also nice. From back of the dump truck to the cab! Overall great product.
T**X
Works
The long cord is really nice
B**N
Great test light. Only one I use.
My first one of these was a Matco branded one Same exact. That one Lasted for 10 years of steady use on trailers, trucks and excavators, until it lost connection in the coiled wire somewhere. Easily my favorite test light with Plenty of length to follow wires. Worth every penny.
J**R
I do like the long cord and it does help a lot
I do like the long cord and it does help a lot . The shipping was quick and product arrived promptly . However I just wish it was not made in china .
C**W
Best test light I've ever bought
I work on buses and at times a good ground is a long way off but with this light it's no problem and the quality is unbeatable. OTC has made tools for commercial use for many years and what I have used over the years has always been high quality.
G**S
Very well built test light
Needed a longer cord on my test light, my old one has a much shorter cord and shorter overall size. Old test light is also 12 volt. This test light is much bigger than my older test light and works perfectly for my application. I needed to reach down into a very constricted area and the added length works well for that. Ground clamp is well made and quite sturdy. Expect that this light will be trouble free for years to come.
J**Y
Reach those hard to find places
Great having a long lead for a large vehicle. Finding a good ground on a large vehicle can be a challenge when you want to test a circuit on a large vehicle. This works well. The point on the tester is easy to work with on circuit boards and easy to puncture wire insulation to a quick test. I found I like this better than the small ones and use it to check all my DC connections and fuses. Clip is big enough to grab on to a lot of large steel or small enough to grab a small screw or wire.
J**.
My favorite test light.
This is my favorite test light. I’ve used a bunch in my career as a diesel tech. This ones the best. Long cord and a clip that you can actually clip on stuff. Occasionally the bulb looses contact but all You have to do is unscrew it and screw it back together and that will get it working again.
D**E
This is a professional grade test light that draws 60mA at 12.5V, so it has more dynamic resistance compared to the older 3636 OTC tool that draws 150mA. Interestingly the higher resistance is mostly from the replaceable white incandescent bulb, and the new 3642 bulb is the same size (27mm long) and interchangeable with the older classic 3633 red bulb. So if you want more current you can swap in an old bulb. I'll guess the new bulb is likely more robust simply because it draws a lot less power so won't get as hot. I did a 1 min review of how this test light performs on a variable power supply, titled "a tradesman knows his tools", or search OTC 3642. Overall I'd call this a winner, there is a smooth drop in brightness as voltage falls, becoming almost unnoticeable at 5 volts. Clamp is robust and the whole thing has pro level quality. Cord stretches to 24 feet.
B**N
Just have to test for s couple of seconds, so power can travel through the long cable!
E**C
Nothing negative to report. Works as intended
W**L
Looks well built and has a nice long cord in it
S**T
fast delivery ...OTC quality ... great product ..
Trustpilot
2 weeks ago
1 month ago