The LED Keeper Pro uses insulation piercing to connect to the copper within the light set wires and illuminate functioning sections by creating mini-circuits. Success is achieved through the process of elimination.Only tool able to diagnose and repair LED light setsPlace markers provided to assist in testingAssists with sets that have replaceable and non replaceable bulbsIncludes place markers, bulb and fuse tester, bulb puller, 9 V battery and universal bulb replacement POD