OTC Tools OTC 3633 Mini Circuit Tester. OTC Tools. Small handle with needlepoint stainless steel probe allows easy back probing and piercing. Special threaded probe comes with screw on alligator clip for additional versatility. Useful in testing electrical circuits and locating shorts, grounds, and open circuits. Features and Benefits 12', heavy-duty, red coil, cord lead. Checks 6- and 12-volt systems. Ergonomic, slim designed clear handle. Bright red, high intensity/slim style replaceable bulb. Positive contact-molded strain relief. Heavy-duty, stainless steel probe with insulated shaft. Heavy-duty clip with positive soldered connection. Email for product availability.