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Charge circuit diode by John DeHaan
Started on: 02-17-2014 04:48 PM
Replies: 12 (376 views)
Last post by: CowsPatoot on 02-19-2014 09:32 PM
John DeHaan
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Report this Post02-17-2014 04:48 PM Click Here to See the Profile for John DeHaanSend a Private Message to John DeHaanEdit/Delete MessageReply w/QuoteDirect Link to This Post
According to the factory wiring diagram, there is a diode located in the wiring harness between the charge lite and the alternator. Does anyone know exactly where it is located?

info:
86 V6 Fiero gt
new alternator
charging voltage is 14.65 V (high)
charge lite stays dimly lit when running.

John(Mongo)
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olejoedad
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Report this Post02-17-2014 05:27 PM Click Here to See the Profile for olejoedadClick Here to Email olejoedadSend a Private Message to olejoedadEdit/Delete MessageReply w/QuoteDirect Link to This Post
The 86 Factory Service Manual calls out the location as "In main harness, below rear bulkhead grommet".
IIRC, it is on the inside of the passenger compartment, passenger side grommet, about 6" away from grommet. Look for a brown wire with a tape bundle......
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theogre
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Report this Post02-17-2014 11:00 PM Click Here to See the Profile for theogreClick Here to visit theogre's HomePageSend a Private Message to theogreEdit/Delete MessageReply w/QuoteDirect Link to This Post
bulb diode likely not your problem.

14.65 is normal

bulb on likely means Alt with problems. Alt is new but still check alt for bad alt diodes etc. New and Rebuild can be bad right out of box.
Check side plug for iffy wire or connection(s).

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Patrick
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Report this Post02-18-2014 03:04 AM Click Here to See the Profile for PatrickClick Here to Email PatrickSend a Private Message to PatrickEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by John DeHaan:

According to the factory wiring diagram, there is a diode located in the wiring harness between the charge lite and the alternator. Does anyone know exactly where it is located?


From a couple weeks ago...

 
quote
Originally posted by Patrick HERE:

THIS particular thread is good.

[This message has been edited by Patrick (edited 02-18-2014).]

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fieroguru
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Report this Post02-18-2014 06:22 AM Click Here to See the Profile for fieroguruSend a Private Message to fieroguruEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by olejoedad:

The 86 Factory Service Manual calls out the location as "In main harness, below rear bulkhead grommet".
IIRC, it is on the inside of the passenger compartment, passenger side grommet, about 6" away from grommet. Look for a brown wire with a tape bundle......


It looks like this:

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fieroguruperformance.com

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IXSLR8
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Report this Post02-18-2014 10:47 PM Click Here to See the Profile for IXSLR8Click Here to Email IXSLR8Send a Private Message to IXSLR8Edit/Delete MessageReply w/QuoteDirect Link to This Post
What is the diode supposed to do in the circuit? Is it just keeping voltage going one direction or?

We have a battery drain in our 85GT N* conversion which I believe is the new Caddy alternator. It drains only on the alternator. We have replaced it twice (with the same brand) and it continues to do the same and charges inconsistently at idle...lights getting brighter and then duller. It seems to be more consistent at driving speeds.

Could it be a bad diode in our car allowing voltage to go both directions?
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AL68
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Report this Post02-18-2014 11:19 PM Click Here to See the Profile for AL68Click Here to Email AL68Send a Private Message to AL68Edit/Delete MessageReply w/QuoteDirect Link to This Post
Had same problem with my 86 GT - light glowed but charged ok, diode trio in alternator was bad - part was about $4 at NAPA.
To test - unplug alternator & start car - if light is off diode trio is bad.
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CowsPatoot
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Report this Post02-19-2014 03:18 AM Click Here to See the Profile for CowsPatootClick Here to visit CowsPatoot's HomePageSend a Private Message to CowsPatootEdit/Delete MessageReply w/QuoteDirect Link to This Post
I don't agree with your test, AL68. That light needs a completed circuit in order to glow. By unplugging your alternator, you are breaking the circuit regardless of what is causing it to glow.
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olejoedad
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Report this Post02-19-2014 06:59 AM Click Here to See the Profile for olejoedadClick Here to Email olejoedadSend a Private Message to olejoedadEdit/Delete MessageReply w/QuoteDirect Link to This Post
To excite the field and start producing voltage, the wires on the small plug to the alternator must have 12 volts. One wire is always hot, the other wire sees voltage when the key is turned on, via the GAGE fuse cicuit, thru the VOLT meter and CHARGE light.
Unplugging the alternator and starting the car will result in a NO CHARGE condition.
A diode is simply an electrical check valve. It was not used in the 88's.
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theogre
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Report this Post02-19-2014 09:20 AM Click Here to See the Profile for theogreClick Here to visit theogre's HomePageSend a Private Message to theogreEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by olejoedad:
To excite the field and start producing voltage, the wires on the small plug to the alternator must have 12 volts. One wire is always hot, the other wire sees voltage when the key is turned on, via the GAGE fuse cicuit, thru the VOLT meter and CHARGE light.
Unplugging the alternator and starting the car will result in a NO CHARGE condition.
A diode is simply an electrical check valve. It was not used in the 88's.

Iffy side plug or wire to it can stop alt to charge.
See my Cave, Alternator Sense

Most often Diodes fail in Open condition and Lamp etc connected to it/them Will Not light.
This is why I said above Lamp diode isn't the problem. If diode is shorted you could see negative volts from volt meter across the lamp. (Make sure meter black goes to ground. Don't pull the lamp. Measure at dash circuit "board.")

Diode Trio fails same Open condition most time. A shorted Diode can drain the battery.
Call a trio but uses 6 diode... Diode Trio because Three Phases AC from Alt's windings to rectify.
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John DeHaan
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Report this Post02-19-2014 01:07 PM Click Here to See the Profile for John DeHaanSend a Private Message to John DeHaanEdit/Delete MessageReply w/QuoteDirect Link to This Post
Thanks fellas, Turns out the new Alt was defective.
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AL68
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Report this Post02-19-2014 08:58 PM Click Here to See the Profile for AL68Click Here to Email AL68Send a Private Message to AL68Edit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by CowsPatoot:

I don't agree with your test, AL68. That light needs a completed circuit in order to glow. By unplugging your alternator, you are breaking the circuit regardless of what is causing it to glow.


Exactally - by unplugging it you eliminate problems in the rest of the circuit from the alternator to the dash light. The glowing light is caused by a partially shorted diode trio in the alternator.

In the Fiero alternator circuit the bulb needs a ground to light, if unplugging the alternator turns off the light the problem is in the alternator. If the light is still on or glows the wiring is shorted to ground somewhere else, the alternator may be ok.
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CowsPatoot
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Report this Post02-19-2014 09:32 PM Click Here to See the Profile for CowsPatootClick Here to visit CowsPatoot's HomePageSend a Private Message to CowsPatootEdit/Delete MessageReply w/QuoteDirect Link to This Post
I see what you are saying. I agree that the test indicates that something inside the alternator casing is bad...just don't agree that it zeros in on the diode trio specifically.
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