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Battery idiot light on - whats the problem - help!


98v70dad

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Just a heads up about "new" parts
Labor is expensive, materials are cheap

So there is no "Quality Control" testing done on assembled units any longer, well unless you buy AC/Delco or Motorcraft units, car makers still pay extra for Quality Control, which makes their parts much more expensive, but they can't afford a batch of bad units installed in new vehicles

So never assume the "new" part works as it should, just because its "new"
In the case of alternators you just need to test 3 of the vehicles wires, if they test OK then a working alternator will "work"
If alternator doesn't work then return it
Yeah, I know. At one time I used to specify parts for commercial airplanes. I worked for an airline and bought some expensive stuff. Airplane parts cost a lot. Like $250,000 is not unusual. When you're spending that much money and screw up the boss notices. In this case I'm my own boss and I'm only pissed at myself for just assuming that the oem alternator was the reason for my problem. Anyhow I'm not a mechanic and I should have done more troubleshooting as you suggested because my idiot light is still lit.

I replaced the alternator and recharged the battery and it blew the 15A alternator fuse under the hood immediately The fusible link has continuity and the new battery is fully charged, although its only showing 12.7 volts and its only about a month old. I am a little unsure what to try next.

Remy used to be called Remy-Delco. The alternator is identical to the AC Delco part and seems to be high quality. Every one of them is bench tested by running it up and making sure it works before its shipped. Every alternator comes with a test report of all the important metrics. I now suspect the Walmart battery. They get very good reviews but its the first one I've ever bought. I used to buy NAPA 72 month batteries until the last three failed well short of the expected time. The last one I bought didn't make it 2 years - barely more than one.

If anyone can tell me what to try next I'd appreciate the suggestions.
 


RonD

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...................new battery is fully charged, although its only showing 12.7 volts..............thats correct for a new battery....engine OFF

Engine running battery should show 13.5 to 14.5volts if alternator is working

Test the 3 wires as said
If they test OK then no matter what the alternator is bad, its not a maybe or a guess

Bench test doesn't show a "good" alternator, it can show a bad alternator, but not always

Charging systems are very simple, do over complicate it
 

98v70dad

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...................new battery is fully charged, although its only showing 12.7 volts..............thats correct for a new battery....engine OFF

Engine running battery should show 13.5 to 14.5volts if alternator is working

Test the 3 wires as said
If they test OK then no matter what the alternator is bad, its not a maybe or a guess

Bench test doesn't show a "good" alternator, it can show a bad alternator, but not always

Charging systems are very simple, do over complicate it
If I put in a new fuse it blows immediately. So, I don't know what voltage I'm getting with the engine running.
 

RonD

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Unplug the 3 wire connector on alternator

Put in a 15 amp fuse in the engine fuse box and see if it blows, if not then Alternator has an internal short, its bad, take it back

If it does blow then the Yellow/white stripe wire on the 3 wire connector has a short
Follow it, you will have to untape the harness, so have some new tape handy
If there is any obvious place on the harness that looks damaged then start there

Its a yellow/white stripe wire all the way to the fuse box



You can by pass this wire with an inline 15amp fuse on the alternator
Cut the Yellow wire and splice the end that goes to 3 wire connector to fuse holder, hook other end of fuse holder to B+ terminal on the back of the alternator, plug in 3 wire connector, insert fuse
All done

This Yellow wire is the Monitor for voltage regulator, it tells regulator if battery is recharged and if Headlights are on or fan is on high, so not a high amp circuit, and it just need to be hooked to battery, like B+ wire is
 
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98v70dad

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Unplug the 3 wire connector on alternator

Put in a 15 amp fuse in the engine fuse box and see if it blows, if not then Alternator has an internal short, its bad, take it back

If it does blow then the Yellow/white stripe wire on the 3 wire connector has a short
Follow it, you will have to untape the harness, so have some new tape handy
If there is any obvious place on the harness that looks damaged then start there

Its a yellow/white stripe wire all the way to the fuse box



You can by pass this wire with an inline 15amp fuse on the alternator
Cut the Yellow wire and splice the end that goes to 3 wire connector to fuse holder, hook other end of fuse holder to B+ terminal on the back of the alternator
All done

This Yellow wire is the Monitor for voltage regulator, it tells regulator if battery is recharged and if Headlights are on or fan is on high, so not a high amp circuit, and it just need to be hooked to battery, like B+ wire is
Thanks. That's a clever repair. I was just out in the driveway with a flashlight looking at the wire harness after studying the wiring diagram. The harness snakes thru and under and around a lot of stuff. Since its 23 years old the covering is brittle. It would be tough to find a short without completely tearing it up so I'll use your bypass idea if I need to do that. I have always liked working on cars but you can probably tell that I am not good at electrical at all.

Could I also get some idea if the yellow wire has a short by doing a continuity test between the connector at the alternator end and the fuse panel with the fuse removed?
 

Josh B

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A short in that would still allow continuity, only a complete break in it would show none
 

98v70dad

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RonD

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Not my clever idea :)
Thats how alternator's were/are wired some years, with a Fusible link between B+ and the Yellow wire terminal on alternator
And all "one wire" alternators are wired that way

If fuse blows with connector unplugged then it is shorted to ground, you could test from fuse to connector but already know there is a problem with the wire, so.................
Just test from connector to alternators case, would show close to 0 ohms because wire is grounded
But neither tells you where.................
 

98v70dad

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Not my clever idea :)
Thats how alternator's were/are wired some years, with a Fusible link between B+ and the Yellow wire terminal on alternator
And all "one wire" alternators are wired that way

If fuse blows with connector unplugged then it is shorted to ground, you could test from fuse to connector but already know there is a problem with the wire, so.................
Just test from connector to alternators case, would show close to 0 ohms because wire is grounded
But neither tells you where.................
So today I put in a new fuse and it didn't blow. I decided as a last effort I would unplug the wires from the alternator and give the connectors a good heavy spray of electrical contact cleaner. I did that three times and let it dry thoroughly. I plugged it back together fired it up and the battery light was out. 14.4V at the battery with the engine running. I went on a 30 mile test drive with the lights on and the battery is still fully charged Can't really explain it but it seems to be fine now. Maybe the connector was shorted internally by the oil I spilled on it. I wiggled the wire harness quite a bit in all directions thinking that there might be a short near the end connector but it doesn't seem to be the case.

I learned a good bit from asking questions and appreciate the help i got. I'm not convinced that I found the problem but at least for today it seems that I just had an oil fouled connector.
 

RonD

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Good work (y)
 

98v70dad

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Good work (y)
Well, hopefully there isn't a short in the wire harness that corrected itself temporarily by moving it. Time will tell I guess. If there still is a short its in the first 6 or inches.
 

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