OTC Tools OTC 3636 Heavy Duty Coil Cord Circuit Tester. OTC Tools. Designed for testing electrical circuits and locating shorts, grounds, and open circuits. Features and Benefits 12-foot, heavy-duty, red coil cord lead. 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.