Mechanics That Have No Specialised Diagnostic Equipment, But Need To Check The Status Of The Engine Management System Before Service Work . Mechanics That Are Skilled In Diagnostics But Need A Very Quick Test Tool Before Becoming More Deeply Involved. The Tester Has A Simple Cable With Croc-Clip Battery Connection And One Signal Lead Terminated With A 4 Mm Plug. The User Will Need To Connect The Signal Plug To The Harness And We Recommend The Use Of Mini Break-Out Boxes Or Wire-Piercing Probes. These Connectors And Probes Are Not Included In The Kit To Keep The List Price At A More Modest Level, And Because If A User Purchases More Than One Type From This Series He Would Replicate The Connectors Several Times. What this tool is for: This tool allows you to get a quick check of the quality of the electrical signal arriving at each injector in a petrol engine management system, multi-point or single-point.When to use this tool: When a vehicle has poor hot or cold starting When a vehicle has poor fuel consumption, When a vehicle fails to start but the engine will crank, When a vehicle starts but stalls some time later. How to connect the tool:Connect the croc-clips to the positive [red] and negative [black] terminals of the vehicle battery. A healthy power connection is shown by a green Power LED. The recommended method of connection to the harness is to use a suitable break out box [SP Part No 30080000 Interface Lead Set]. When this is not possible, an insulation piercing probe [SP Part No 30050300 Cables Probes Insulation Piercing] can be employed providing the usual precautions are taken to avoid cable damage. Injectors generally have 2 wires and there is no certain way of deciding which wire is the active one so trial and error must be used. The Tester will normally indicate a signal present ONLY if connected to the active wire with the engine running so if no lights are shown [apart from the Power], try the other wire.