You are testing a computer circuit that is a part of the fuel injection system. What is the best instrument to use?

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When diagnosing a fuel-injection computer circuit, you want a quick, straightforward check to confirm that the circuit is being energized or switched as commanded. A digital test light is ideal for this because it gives an immediate, visible indication of voltage presence with minimal setup. By connecting it to the circuit at the appropriate point, you can see whether power is reaching the ECU output or whether a line is being driven to ground when expected. This lets you quickly determine if the fault lies in wiring, connectors, or the module’s output drive, without needing to measure exact voltages or capture fast-changing signals. If you need precise voltage levels, resistance, current, or waveform timing, you’d switch to a multimeter or oscilloscope, but for a fast yes/no indication of energization, the digital test light is the simplest and fastest tool.