DGP301 Glow Plug Tester provides fault detection thru LED's for a quick analysis of short circuit over current normal operation and open circuit/under current Tester allows for testing without removing glow plug from engine and powers the glow plug to test the plug in its operating state Much more accurate test 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 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; Push the contact plate in the end of the test probe onto the glow plug; Terminate until the glow plug has warmed up. This might take between 3 and 20 seconds (Check manufacturers specs for exact warm-up time) Check which LED is illuminated on the control panel; NOTE:Even all 4 glow plugs are open circuit, DO NOT assume this tool is faulty. The vehicle might be still started up with all 4 glow plugs being defective. Due to different batches, there may be differences in product appearance, color, and printed text, which will not affect the use. Colour:Black Material:Plastic Package Contents: 1 * Tester Only the above package content, other products are not included. Note: Light reflection and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm.