How To Troubleshoot If Alternator Is Bad. Repeat the step 3 but this time use the voltmeter test and touch the battery negative post and the alternator. If the voltage dropped back into the 12’s, it’s a very strong indication that the alternator is bad.
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While checking, ensure that the engine is off. Just remember that the negative battery cable doesn’t go to the dead battery negative terminal (this is a common mistake!). Charging output can be tested on a vehicle with a digital voltmeter.
Repeat the step 3 but this time use the voltmeter test and touch the battery negative post and the alternator. Check the battery ground connection; If the belt is loose, you can try tightening it by adjusting the alternator on its mounting bracket.
After doing so, observe your readings once again. Several symptoms of a bad alternator include a dead battery and other electrical problems, such as the radio This is why a physical examination is important.
The belt is too loose, so it slips on the pulleys instead of traveling along them. You will need a wrench or socket set to accomplish this. While checking, ensure that the engine is off.
Just remember that the negative battery cable doesn’t go to the dead battery negative terminal (this is a common mistake!). If you see a voltage drop, the alternator needs an inspection. Clamp it to an unpainted metal surface on the dead car.
Make sure you have good ground connections at the alternator (alternator case) and voltage regulator, especially if your vehicle uses a remote voltage regulator. When an alternator goes bad what happens? Check for a bad alternator voltage regulator and circuit.