Noid Light
A diagnostic indicator light plugged into a fuel injector harness to test if the ECU is sending the proper electrical pulse to fire the injector.
A noid light is a simple, highly effective diagnostic tool used to test the electrical control circuit of electronic fuel injectors. It consists of a small bulb or LED mounted in a plastic socket with pins that plug directly into the fuel injector harness connector in place of the injector.
To test the circuit, the noid light is plugged in and the engine is cranked. If the ECU is successfully grounding the injector circuit to pulse the injector, the noid light will flash rapidly. A steady flash indicates the injector driver circuit, wiring harness, and engine computer are operating correctly, suggesting the misfire is caused by a mechanical issue or a clogged injector nozzle.
If the light does not flash, it indicates an electrical fault: a blown fuse, broken wiring harness, or a failed driver inside the ECU. Noid lights come in kits with various connector shapes to fit different manufacturer designs, providing an essential diagnostic tool for troubleshooting crank-no-start and misfire conditions.