Diesel Glow Plug Tester Glow Plug Tester provides fault detection through LED's for a quick analysis; Short Circuit, Over Current, Normal Operation, Open Circuit/Under Current.. Glow Plug Tester allows for testing without removing glow plug from engine. . Powers the glow plug to test the plug in it's operating state. . Test much more accurate than a cold resistance test, which can miss short circuits. . Tester uses a current measurement to accurately determine proper operation and check for short circuits. 3673