QUICKLY TEST RELAYS OUTSIDE OF THE VEHICLE to check coil and switch contact functionNO NEED TO CLAMP TO BATTERY - self-contained, accurate testing with instant resultsGREEN LED PASS & RED LED FAIL clearly indicates good or bad relay conditionTESTS MOST COMMON 12 VOLT 4 & 5 PIN 汽车用品 RELAYS found on today's vehiclesCOMPACT, ALL-IN-ONE DESIGN powered by included AA batteries