How to Test a Lucas Alternator
- 1). Lift the hood of your car and prop it up. Locate the battery, a solid, rectangular block usually on the driver's side of the engine near the fender. The battery may have a plastic cover, held down by a clip or screwed in place. Remove the cover.
- 2). Connect the voltmeter to the battery posts. The voltmeter has a positive and negative lead, which are red and black, respectively. Attach the positive lead to the positive battery post, which had a red battery cable connector and a "+" sign beside it, then attach the negative lead to the negative battery post, which is black and has a "-" sign beside it.
- 3). Make a note of the initial reading on the voltmeter while the engine is off. This is a measurement of the voltage in the battery and should be between 12.5 and 12.8 volts. If it's significantly less, the trouble could be your battery and not your alternator. Even a brand-new alternator can't recharge a dead battery.
- 4). Start the engine and look at the voltmeter again for the new reading. This time the voltmeter is measuring the voltage in the alternator, because with the engine running, the alternator is supplying the battery with power. A good alternator has a reading of between 13.6 and 14.3 volts. Anything less is a sign of trouble.
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