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Pulsing headlights

1998 Nissan Sentra, 1.6L 4cyl Automatic, 107K miles. My headlights, dash and tail lights are pulsing occasionally, at a stead cycle like about 60 per minute. Its not a random flicker but a steady pulse. My mechanic just started looking at it and is going to eliminate possibilities one by one, first by checking the grounds. He put a simple continuity light across the battery posts and saw a visible pulse in its lamp. Another place did a quick check of just the battery and while it had a good charge it indicated that the health was “zero”, meaning real bad. Others have suggested a bad diode in the alternator. So whats going on?

The alternator is about to die, and I would suggest that you replace it before you become stranded when it suddenly stops functioning totally. Also, since you need a new battery, you will quickly kill the new battery if you don’t replace the alternator now.

I agree. You need a new alternator and a new battery. Your mechanic should have tested both immediately.

He had the multimeter, and he didn’t check for a/c voltage from the alternator?

Added: he used a test light, not a multimeter. You can’t detect a/c with a test light. You can’t do much “mechanicing” without a multimeter, either.

The only thing I can’t figure out is why after having it looked at twice you’re still asking the question. You’ve been told you need a new battery and a new alternator. Simply get them replaced.

same thing happen to me. it was diode in alternator. problem solved. good luck