DGP301 Glow Plug Tester provides fault detection through LEDs for quick analysis of short circuit, over current, normal operation, and open circuit/under current. Tester allows for testing without removing the glow plug from the engine and powers the glow plug to test it in its operating state. More accurate than a cold resistance test, which can miss short circuits. Tester uses current measurement to accurately determine proper operation and detect short circuits. OPERATING INSTRUCTIONS: Designed to work on 12V only. Disconnect the busbar or leads from the glow plugs to be tested. Connect the red battery clamp to the positive terminal of the battery, and the black battery clamp to the negative terminal of the battery. Press the contact plate of the test probe onto the glow plug. Wait until the glow plug has warmed up. This may take between 3 and 20 seconds (refer to manufacturer specifications for exact warm-up time). Check which LED is illuminated on the control panel. Note: Even if all 4 glow plugs are open circuit, do not assume the tool is faulty. The vehicle may still start with all 4 glow plugs defective. Due to different production batches, there may be variations in product appearance, color, and printed text. These variations do not affect functionality. Color: Black Material: Plastic Package Contents: 1 x Tester Note: Light reflection and differences in display screens may cause slight color variations between the product image and the actual item. Measurement error allowance is +/- 1-3 cm.