Lights Are Pulsing.

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Oct 30, 2020 | 10:50 PM

woodsmoke

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Tuned

Joined: Jun 2008

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From: WACO

Lights Are Pulsing.

That's the only way I can explain it. 1966 F-100. 351 Windsor. Alternator. At idle all the lights have a slight pulse. Barely noticeable but can see. Like a heartbeat. Sometimes the alternator light in dash flashes. But. Alternator is charging.. Any ideas as what could be causing this phenomenon?

Oct 30, 2020 | 11:24 PM

Christmas

Logistics Pro

Joined: Jun 2018

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Poor grounds will cause it. Can't have enough grounds.

Oct 31, 2020 | 05:31 PM

john jamieson

Cargo Master

Joined: Jul 2015

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From: tucson

Mine used to pulse and dim at idle, so I did up a relay harness so the headlights get power from the battery when on and not the circuitous route through the old wiring. No more dimming or pulsing. X2 or three on the grounds and other connections.

Nov 1, 2020 | 06:25 AM

robertrpeak

Tuned

Joined: Jul 2016

Posts: 469

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From: TN.

After you clean all the grounds and it still pulse's, get a new alt.

Nov 1, 2020 | 08:27 AM

FordsOnlyGarage

Tuned

Joined: Mar 2017

Posts: 256

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Do a voltage drop test on both positive and negative side of the charging system.

With digital volt meter, check "ground to ground" and "positive to positive" You shouldn't see more than a few tenths of a volts (with the truck running and charging). If more than 1/2 volt, start checking/cleaning connections and grounding points (including the voltage regulator)
If these are good, you likely have a bad diode in the alternator. If you check your amperage output, you will find it's about 2/3 of rated (eg, 65 amp alternator, max output will be about 45amps). Replace the alternator.