Author Topic: Pulsating headlights  (Read 196 times)

Offline thenewbie

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Pulsating headlights
« on: June 04, 2020, 11:53:11 AM »
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.

Offline FlatBlack77

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Re: Pulsating headlights
« Reply #1 on: June 04, 2020, 12:09:40 PM »
Sounds like a bad alternator.

Alot of auto parts stores will test your charging system for free.
"When you are a hammer, everything looks like a nail"
'77 C/10 - 350/350 mild street motor

Offline thenewbie

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Re: Pulsating headlights
« Reply #2 on: June 04, 2020, 12:31:02 PM »
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?

Offline bd

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Re: Pulsating headlights
« Reply #3 on: June 04, 2020, 05:24:24 PM »
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?
Rich
It's difficult to know just how much you don't know until you know it.
In other words... if people learn by making mistakes, by now I should know just about everything!!!
87 R10 Silverado Fleetside 355 MPFI 700R4 3.42 Locker (aka Rusty, aka Mater)

Offline Mike81K10

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Re: Pulsating headlights
« Reply #4 on: June 04, 2020, 07:11:41 PM »
Agree with bd, about the regulator probably being bad. Take it into an auto parts store, they will normally check it for free.

Offline thenewbie

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Re: Pulsating headlights
« Reply #5 on: June 05, 2020, 09:15:28 AM »
Will do, thanks guys. I'll update this when / if i get any results.

Offline 1978C201964

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Re: Pulsating headlights
« Reply #6 on: June 06, 2020, 05:23:36 AM »
Upgrade to a direct battery headlight harness.They are very cheap .YouTube has several videos.