DGP301 Glow Plug Tester provides fault detection thru LED's for a quick analysis of short circuit over current normal operation and open circuit or 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 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 x 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.