The Monster MST75 Relay Circuit Tester quickly and easily identifies problems in vehicle circuits with the push of a button. Help isolate problems in wires, relays or parts when diagnosing a circuit without use of multimeter. This tester includes five vehicle-specific relay connectors, and one universal connector. The MST75 has open ports that can be used as a break out box by users, in combination with other testers. LED lights indicate continuity and current. This tool eliminates the need to use a multimeter to test components and wiring harnesses separately.