Pulsating dashlights
Thread Starter
Instructor
Joined: Apr 2003
Posts: 111
Likes: 0
From: St Louis MO
Pulsating dashlights
1991 L98, 90,000 miles
For a while my dashlights have been pulsating in time with engine rpm. I took my alternator to Advanced Auto to get tested, the chick said it was putting out enough amps and that it was ok. I asked her if there were any other tests that might show some other problem with it such as the regulator acting funny and she said no.
If it's not the alternator, what else could it be? Could it be the alternator?
For a while my dashlights have been pulsating in time with engine rpm. I took my alternator to Advanced Auto to get tested, the chick said it was putting out enough amps and that it was ok. I asked her if there were any other tests that might show some other problem with it such as the regulator acting funny and she said no.
If it's not the alternator, what else could it be? Could it be the alternator?
Le Mans Master
Joined: Jun 2002
Posts: 6,097
Likes: 0
From: High Plains Drifter Fayetteville, AR
I had the same thing since I bought my car. The dash lighting and LCD would flicker. I had to replace the alternator recently and the problem went away, now it's a steady illumination.
Team Owner
Joined: Mar 2001
Posts: 54,124
Likes: 30
From: Cincinnati, Oh USA
Flickering dash lights can be caused by an oscillating voltage regulator in your alternator. One easy test is to unplug the alternator while the engine is running and see if the flickering stops. If it does, replace the voltage regulator or the entire alternator. Parts places that test alternators measure the dc output of the alternator and do not look at the output waveform so they will not be able to tell if the voltage regulator is oscillating. Most ignition analyzers allow you to look at the waveform of the voltage across the battery, mainly to see if the ripple that is normal from the alternator is missing a phase indicating a bad diode. Hope this helps.
Melting Slicks
Joined: Dec 2004
Posts: 2,954
Likes: 2
From: Obama=death for America
Sounds like the internal regulator of your alternator. It would probably be cheaper to have your regulator changed than buy a new alternator. I just had my entire alternator rebuilt. The brushes, regulator, etc. were changed and I only paid $45.
Call Jerry at 941-922-2709. Send him your alternator and he'll send you a rebuilt one for a great price. He does great work. Turnaround is fast too. He did mine.
Call Jerry at 941-922-2709. Send him your alternator and he'll send you a rebuilt one for a great price. He does great work. Turnaround is fast too. He did mine.
Team Owner
Joined: Mar 2001
Posts: 54,124
Likes: 30
From: Cincinnati, Oh USA
Have them watch your dash lights before and after you unplug the alternator with the engine running. Or, show them the alternator output waveform with an oscilloscope. Or, using a large non polarized capacitor like a 1 or larger microfarad capacitor in series with a VOM set to ac volts, measure the ac voltage across your battery with the engine running and compare that with a car with no flickering. The ac voltage should be less than 0.1 volts and from one measurement I have made, the oscillating voltage regulator caused about 1 volt ac ripple from the alternator. The capacitor insures that the ac voltmeter you use does not respond to the 12v dc component out of the alternator as some voltmeters will.
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