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Old 02-27-2007, 01:40 PM
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Someone Please help with GM Alternator

I need help badly.
I have a '64 El Camino which was in serious need of wiring repair when I got it. Horn didn't work, Wipers didn't work, When you pressed the brake pedal both turn indicators on the dash lit up.
I decided the best course of action was a complete re-wire, so I bought a Painless 12 circuit muscle car (generic) wiring harness. I think I put everything together right, but now the alternator is charging 17, sometimes 18 volts. My first thought was voltage regulator(external reg), didn't help. So now I've installed a NEW alternator. Still didn't help.
Also, I've noticed that when I turn on a turn indicator the battery light in the dash lights up with the flashing light.
One day last week I started to drive the car to work at 5:30am, but when I turned the headlights on they sorta brightened & dimmed rythmically, every second or less.

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Old 02-27-2007, 03:35 PM
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Doc here,

First of all, Check the Belt for tightness, Battery cables for clean, tight connections,

THEN. Check all the grounds, Battery to Block At or near the starter, Cable from Block to frame, 10 gauge wire to the Firewall AS well as The Alternator Ground lug, use star washers and burnish ground areas from paint and grease..This may be part of the problem..

Next be sure your DVOM has fresh battery's in it, and is accurate..(test it on a known good vehicle) , Place your DVOM across the battery, with the vehicle warmed and at Idle and at no load..

Your reading should be around 13.95 to 14.4 Volts..If you are STILL reading 17 Volts, Your regulator may need adjustment, on the Field relay contact or the air-gap, (unless it is electronic) OR it may need replacement (New "Bad" ones do happen)

The MOST probable Cause is the Alternator has a failing Diode array, and is NOT rectifying a full 14 volts..If a partial reverse bias on any part of the diode array , ( 6 in total).

An amount of RAW AC will be induced into the system, On a Cheaper Voltmeter, it will read about 17 volts (Set in DCV Scale), or ABOUT the root mean square of 14 volts DC, as AC and DC on the Same line..

the DC will actually be around 11 volts, The rest is useless Harmful AC, being induced into the System.

This AC is Harmful to any linear Op-amps, HMOS,CMOS, Chips (Or Electronic equipment) in the system. Chips of this type architecture won't tolerate AC on a power leg at all, they will go into thermal overload and will shut down (sometimes forever) Computers, Engine modules, Tach's, CD / Radio players , Alarm systems, Digital Gauges, and digital clocks all are at risk. So It's a problem you want to address..

The Battery, although it says 17 volts, won't be charging to full capacity, (Because it is only getting about 11 USEFUL volts DC, ) and the Charge lamp will flash on and off.

Rebuild or take the Alternator back. It is defective.

This should cure the problem..Regulator check first, then alternator.

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