Tests round 7 Pin connectors with flat pins. Each signal from vehicle emits a unique tone. Electric brake control signal illuminates red LED. Time Saver! Just apply brakes, right/left turn signals, running lights, engage reverse and 12 Volt Charging voltage. Loud beep can be heard over shop noise Just plug the Trailer Wiring Buddy into the vehicles trailer harness, go to the driver's seat and operate the controls. Each signal from vehicle emits a unique beep, which can be heard over shop noise. It is simple and easy to use - it saves time! Lighting circuits tested: Left Turn Signal, Right Turn Signal, Brake, Running Lights, Reverse, 12 Volt Charging, Electric Brake Control