OTC Tools OTC 3634 Heavy Duty Straight Cord Circuit Tester. OTC Tools. Designed for testing electrical circuits and locating shorts, grounds, and open circuits. Features and Benefits 5-foot heavy-duty cord. Checks 6- and 12-volt systems. Ergonomic, slim designed clear handle. Bright red, 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.