Astro Pneumatic's 7898 Deluxe Noid Lite & GM AC Signal Test Light Set is the most economic way to check electronic fuel injection (EFI) signals. It allows technicians to quickly and easily check for systems of GM TBI, Bosch PFI Ford TBI, GM PFI, Geo TBI and GM SCPI. Testing is easy - just disconnect the fuel injectors, plug the noid lite into the injector wiring harness, then crank the engine. Normal voltage is indicated by a flashing light, which is visible from passenger compartment. Comes in a blow molded case for easy storage and transport