Alternative Uses of Multimeters: Precautions for Automobile Maintenance
I. Measuring Automotive Resistance with a Multimeter
① When measuring resistance, the component under test on the vehicle must be de-energized and must not be connected in parallel with other electrical components.
② Select the proper range before measuring automotive resistance, and perform ohm zero adjustment on the multimeter within this range. If the multimeter cannot be zeroed, its internal battery is low and needs replacement.
③ When measuring resistance, keep the meter needle around the middle section of the scale to minimize measurement error.
④ Do not use low-resistance ohm ranges below R×100 when measuring low-power transistors, to avoid damaging the transistor due to excessive current.
II. Measuring Automotive Voltage with a Multimeter
① For DC voltage measurement on vehicles, set the selector switch to the V range. For AC voltage measurement, switch to the corresponding position. Select a range matching the measured voltage of the vehicle. If the voltage value is unknown, start with the maximum range for a trial measurement.
② When measuring automotive DC voltage, connect the positive test lead to the high-potential terminal and the negative test lead to the low-potential terminal of the component. If the polarity cannot be determined, briefly touch the two terminals with the test leads for a trial. If the needle deflects toward the negative ("-") side of the DC voltage scale, the leads are reversed.
Reversed test leads may bend the meter needle and cause inaccurate readings. To prevent needle kickback, select a higher range and perform the trial contact quickly.
III. Measuring Automotive Current with a Multimeter
① The multimeter must be connected in series with the component under test on the vehicle.
② For automotive DC current measurement, set the multimeter to the corresponding A range. Connect the positive lead to the high-potential side and the negative lead to the low-potential side so that current flows into the positive lead and out of the negative lead.
③ There is no polarity requirement for test leads when measuring AC current. Select a range matching the measured current. If the current value is unknown, start with the maximum range. When the automotive multimeter is not in use, set the range selector to the highest AC voltage range.
