Measuring the voltage drop When the circuit is powered on, use a multimeter to measure the voltage drop at the ground point, and the reading should be as low as possible. The specific method is: start the engine, use the DC voltage block of the multimeter, touch the red test lead to the output end of the generator, and the black test lead to the engine body, and measure a voltage value; then, use the black test lead to touch the metal part of the frame, and then Measure a voltage value, under normal circumstances, these two values should be consistent, if the former value is large, the latter value is small, the difference is more than 0.5V, indicating that there is a voltage drop of more than 0.5V, which is caused by the engine and the frame. Caused by poor grounding. Note: When detecting the grounding condition of a certain point, the voltage of this point to the positive pole of the power supply should be measured, and try not to measure the resistance of this point to the negative pole of the power supply. This is because the multimeter itself has a certain internal resistance, and the measured resistance value is relatively large.