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73-87 Chevy _ GMC Trucks => Electrical => Topic started by: thenewbie on June 04, 2020, 11:53:11 AM
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Hello all,
New to the forum ( hence the name) and thanks for accepting me. My ride is an 87 gmc v2500. Anyhow, it has a pulsating issue when the headlights are on. The voltmeter will also twitch back and forth. Doesn't do it with just the marker lights on. I've checked all the grounds and they appear to be in good condition. I considered the headlight switch but figured if it was that then the pulsating would also occur when just the marker lights are on. I thought i ask on here before throwing parts at it.
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Sounds like a bad alternator.
Alot of auto parts stores will test your charging system for free.
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I checked the alternator with the truck running, headlights on and got a reading of 14.2 volts at the battery terminals with multimeter. Is there other tests that can be performed before removal and or replacement?
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Is the alternator belt tight? Are the headlamps flaring with constant engine RPM or only as engine RPM changes? Generally, lamp flare at constant engine RPM is caused by a faulty regulator, which is internal to the alternator. What is the charging voltage measured across the battery while the headlamps are flaring? Is it constant or variable?
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Agree with bd, about the regulator probably being bad. Take it into an auto parts store, they will normally check it for free.
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Will do, thanks guys. I'll update this when / if i get any results.
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Upgrade to a direct battery headlight harness.They are very cheap .YouTube has several videos.