Alternator Failure

[Bruce Hart]

On the final leg of a recent trip the alternator was behaving very strange. Watching my volt meter the volts would go to zero and bounce up past 16
volts when the RPMs were under 3000. Above 3000rpm the volt meter would just peg out high. Stopped in NAPA store in Billings and got new
remanufactured alternator. 15 miles down the road and the alternator started behaving the same way, bouncing back and forth from low volts to high
volts. Disconnected center lug of isolator and ran generator until we got home. Tested new exchanged alternator and it was bad. Installed new
remanufactured alternator and only getting 1/2 volt. Checked continuity of wires, getting 11.5 volts to alternator (Battery discharged), APC ok,
Isolator checked out ok, and replaced end connectors. Had the newest alternator tested and it was ok. Cannot figure out why I am only getting 1/2
volt out of alternator. Any ideas. I am going to put another alternator that I know is good and see if that might work.

In the last month and a half this is the THIRD remanufactured alternator that I have replaced. According to the counter person at NAPA I can only get
a 63 amp NEW alternator for the GMC.
Sending another alternator to local rebuilder for testing and repair.

G-genetically
M-modified
C-Chevy
My brother told me this.
--
Bruce Hart
1976 Palm Beach
Milliken, Co

 

[johnny]

There probably wasn't anything wrong with any of those alternators to begin with. However, you lost the reference voltage from the chassis battery.
The usual culprit is the two wire plug on the alternator, but a failure of the isolator diode or a broken wire will give the same result. That it's
intermittent points to the plug. If the sense wire opens, the alternator voltage goes up, trying to get the battery voltage (which it doesn't see due
to the missing connection) up to proper charging voltage. This will cook the house battery and the alternator regulator fairly quickly. Remove the
plug, clean the contacts, tighten them by judicious bending, and check for continuity from one side of the plug to the chassis side of the isolator
with both batteries disconnected and the coach 12v supply turned off. If there is no continuity, trace the wire and fix it. Normally that plug is the
problem you're describing.

--johnny
--
Foolish Carriage, 76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
I forgive them all, save those who hurt the dogs. They must answer to me in hell

 

[john r. lebetski]

I would also examine the isolator and the connections to the horn relay terminal stud.
--
John Lebetski
Woodstock, IL
77 Eleganza II

 

[Ken H.]

Bruce,

Based on the erratic voltage; there's little doubt in my mind that you had
an isolator failure (or a bad cable from the isolator to the chassis
battery). You could probably have saved the alternators by jumping between
the center and the chassis side terminals on the isolator.

Ken H.

On Wed, Jul 10, 2019 at 1:47 PM John R. Lebetski via Gmclist <

> I would also examine the isolator and the connections to the horn relay
> terminal stud.
> --
> John Lebetski
> Woodstock, IL
> 77 Eleganza II
>
>
> _______________________________________________
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>

 

[johnny]

I've never seen an isolator fail intermittently. Intermittents normally point to poor connections. Could be from isolator terminal to the battery
someplace... but that alternator plug is more often the culprit. Simple enough to check both.

--johnny
--
Foolish Carriage, 76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
I forgive them all, save those who hurt the dogs. They must answer to me in hell

 

[Ken B]

I'll second Johnny's recommendation on the alternator plug. I had a similar problem going to a GMCMI rally in Georgia. Upon our arrival, I removed
the alternator. Colonel Ken gave me a ride to the auto parts store. They tested it and gave me a new one. (They did not know how to test it
correctly but I said nothing because I wanted a new one.) Upon installation, it failed exactly the same way. Additional diagnosis, which I should
have done prior to removing the alternator in the first place, found a poor connection at the plug on the alternator. A little additional crimping
pressure applied with a pair of pliers to the female connectors permanently fixed the problem.

Check clean and add additional pressure to the female side on connectors. If you have an APC squeeze those female connectors too.
--
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana

 

[Bruce Hart]

Worked on the charging system all afternoon. Cleaned and wire bushed all
connections, rechecked isolator-ok ,installed charged battery12.7 volts,
Found what I thought was a good alternator was also bad (light circuit
fault), and retested remanufactured alternator and it failed.

Did what Johnny suggested and crimped apc and plug end of wire harness.
Will need another good alternator to see if that effort helped.

Thanks everybody for your input, Emery will help me try to sort this out
tomorrow.

On Wed, Jul 10, 2019 at 7:26 PM Ken Burton via Gmclist <

> I'll second Johnny's recommendation on the alternator plug. I had a
> similar problem going to a GMCMI rally in Georgia. Upon our arrival, I
> removed
> the alternator. Colonel Ken gave me a ride to the auto parts store. They
> tested it and gave me a new one. (They did not know how to test it
> correctly but I said nothing because I wanted a new one.) Upon
> installation, it failed exactly the same way. Additional diagnosis, which
> I should
> have done prior to removing the alternator in the first place, found a
> poor connection at the plug on the alternator. A little additional crimping
> pressure applied with a pair of pliers to the female connectors
> permanently fixed the problem.
>
> Check clean and add additional pressure to the female side on connectors.
> If you have an APC squeeze those female connectors too.
> --
> Ken Burton - N9KB
> 76 Palm Beach
> Hebron, Indiana
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>

--
Bruce Hart
1976 Palm Beach
Milliken, Co
GMC=Got More Class

 

[jim kanomata1]

https://www.gmcrvparts.com/product-p/gm7-028.1.htm

On Wed, Jul 10, 2019 at 7:14 PM Bruce Hart via Gmclist <

> Worked on the charging system all afternoon. Cleaned and wire bushed all
> connections, rechecked isolator-ok ,installed charged battery12.7 volts,
> Found what I thought was a good alternator was also bad (light circuit
> fault), and retested remanufactured alternator and it failed.
>
> Did what Johnny suggested and crimped apc and plug end of wire harness.
> Will need another good alternator to see if that effort helped.
>
> Thanks everybody for your input, Emery will help me try to sort this out
> tomorrow.
>
> On Wed, Jul 10, 2019 at 7:26 PM Ken Burton via Gmclist <

>
> > I'll second Johnny's recommendation on the alternator plug. I had a
> > similar problem going to a GMCMI rally in Georgia. Upon our arrival, I
> > removed
> > the alternator. Colonel Ken gave me a ride to the auto parts store.
> They
> > tested it and gave me a new one. (They did not know how to test it
> > correctly but I said nothing because I wanted a new one.) Upon
> > installation, it failed exactly the same way. Additional diagnosis,
> which
> > I should
> > have done prior to removing the alternator in the first place, found a
> > poor connection at the plug on the alternator. A little additional
> crimping
> > pressure applied with a pair of pliers to the female connectors
> > permanently fixed the problem.
> >
> > Check clean and add additional pressure to the female side on connectors.
> > If you have an APC squeeze those female connectors too.
> > --
> > Ken Burton - N9KB
> > 76 Palm Beach
> > Hebron, Indiana
> >
> > _______________________________________________
> > GMCnet mailing list
> > Unsubscribe or Change List Options:
> > http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
> >
>
>
> --
> Bruce Hart
> 1976 Palm Beach
> Milliken, Co
> GMC=Got More Class
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>

--
Jim Kanomata
Applied/GMC, Newark,CA
jimk
http://www.appliedgmc.com
1-800-752-7502

 

[Bruce Hart]

Tried another alternator with the same results. 1/2 volt output.
Rechecked continuity of both wires in wire harness and wire to center post
of isolator. 12.6 volts going into alternator and only 1/2 volt coming
out. Crimped down on connectors in plug had to use pliers to pull them
apart. Tried without the APC but had same results. At a total loss as what
to do know.

On Wed, Jul 10, 2019 at 11:27 PM Jim Kanomata via Gmclist <

> https://www.gmcrvparts.com/product-p/gm7-028.1.htm
>
> On Wed, Jul 10, 2019 at 7:14 PM Bruce Hart via Gmclist <

>
> > Worked on the charging system all afternoon. Cleaned and wire bushed all
> > connections, rechecked isolator-ok ,installed charged battery12.7 volts,
> > Found what I thought was a good alternator was also bad (light circuit
> > fault), and retested remanufactured alternator and it failed.
> >
> > Did what Johnny suggested and crimped apc and plug end of wire harness.
> > Will need another good alternator to see if that effort helped.
> >
> > Thanks everybody for your input, Emery will help me try to sort this out
> > tomorrow.
> >
> > On Wed, Jul 10, 2019 at 7:26 PM Ken Burton via Gmclist <

> >
> > > I'll second Johnny's recommendation on the alternator plug. I had a
> > > similar problem going to a GMCMI rally in Georgia. Upon our arrival, I
> > > removed
> > > the alternator. Colonel Ken gave me a ride to the auto parts store.
> > They
> > > tested it and gave me a new one. (They did not know how to test it
> > > correctly but I said nothing because I wanted a new one.) Upon
> > > installation, it failed exactly the same way. Additional diagnosis,
> > which
> > > I should
> > > have done prior to removing the alternator in the first place, found a
> > > poor connection at the plug on the alternator. A little additional
> > crimping
> > > pressure applied with a pair of pliers to the female connectors
> > > permanently fixed the problem.
> > >
> > > Check clean and add additional pressure to the female side on
> connectors.
> > > If you have an APC squeeze those female connectors too.
> > > --
> > > Ken Burton - N9KB
> > > 76 Palm Beach
> > > Hebron, Indiana
> > >
> > > _______________________________________________
> > > GMCnet mailing list
> > > Unsubscribe or Change List Options:
> > > http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
> > >
> >
> >
> > --
> > Bruce Hart
> > 1976 Palm Beach
> > Milliken, Co
> > GMC=Got More Class
> > _______________________________________________
> > GMCnet mailing list
> > Unsubscribe or Change List Options:
> > http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
> >
>
>
> --
> Jim Kanomata
> Applied/GMC, Newark,CA
> jimk
> http://www.appliedgmc.com
> 1-800-752-7502
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>

--
Bruce Hart
1976 Palm Beach
Milliken, Co
GMC=Got More Class

 

[Ken H.]

Bruce,

With the battery charged and connected and the ignition on, what's the
voltage at the brown wire in the alternator plug? You need 12 VDC there
(through the 10 Ohm Nichrome wire) to provide initial excitation to the
alternator. Gotta have that before anything else can happen. The 12 VDC
at the white wire in that plug is only there to limit the alternator output
to the charging voltage at the screw lug -- the voltage that you had
dropping out and going high originally.

Ken H.

On Thu, Jul 11, 2019 at 9:31 PM Bruce Hart via Gmclist <

> Tried another alternator with the same results. 1/2 volt output.
> Rechecked continuity of both wires in wire harness and wire to center post
> of isolator. 12.6 volts going into alternator and only 1/2 volt coming
> out. Crimped down on connectors in plug had to use pliers to pull them
> apart. Tried without the APC but had same results. At a total loss as what
> to do know.
>
> On Wed, Jul 10, 2019 at 11:27 PM Jim Kanomata via Gmclist <

>
> > https://www.gmcrvparts.com/product-p/gm7-028.1.htm
> >
> > On Wed, Jul 10, 2019 at 7:14 PM Bruce Hart via Gmclist <

> >
> > > Worked on the charging system all afternoon. Cleaned and wire bushed
> all
> > > connections, rechecked isolator-ok ,installed charged battery12.7
> volts,
> > > Found what I thought was a good alternator was also bad (light circuit
> > > fault), and retested remanufactured alternator and it failed.
> > >
> > > Did what Johnny suggested and crimped apc and plug end of wire harness.
> > > Will need another good alternator to see if that effort helped.
> > >
> > > Thanks everybody for your input, Emery will help me try to sort this
> out
> > > tomorrow.
> > >
> > > On Wed, Jul 10, 2019 at 7:26 PM Ken Burton via Gmclist <

> > >
> > > > I'll second Johnny's recommendation on the alternator plug. I had a
> > > > similar problem going to a GMCMI rally in Georgia. Upon our
> arrival, I
> > > > removed
> > > > the alternator. Colonel Ken gave me a ride to the auto parts store.
> > > They
> > > > tested it and gave me a new one. (They did not know how to test it
> > > > correctly but I said nothing because I wanted a new one.) Upon
> > > > installation, it failed exactly the same way. Additional diagnosis,
> > > which
> > > > I should
> > > > have done prior to removing the alternator in the first place, found
> a
> > > > poor connection at the plug on the alternator. A little additional
> > > crimping
> > > > pressure applied with a pair of pliers to the female connectors
> > > > permanently fixed the problem.
> > > >
> > > > Check clean and add additional pressure to the female side on
> > connectors.
> > > > If you have an APC squeeze those female connectors too.
> > > > --
> > > > Ken Burton - N9KB
> > > > 76 Palm Beach
> > > > Hebron, Indiana
> > > >
> > > > _______________________________________________
> > > > GMCnet mailing list
> > > > Unsubscribe or Change List Options:
> > > > http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
> > > >
> > >
> > >
> > > --
> > > Bruce Hart
> > > 1976 Palm Beach
> > > Milliken, Co
> > > GMC=Got More Class
> > > _______________________________________________
> > > GMCnet mailing list
> > > Unsubscribe or Change List Options:
> > > http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
> > >
> >
> >
> > --
> > Jim Kanomata
> > Applied/GMC, Newark,CA
> > jimk
> > http://www.appliedgmc.com
> > 1-800-752-7502
> > _______________________________________________
> > GMCnet mailing list
> > Unsubscribe or Change List Options:
> > http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
> >
>
>
> --
> Bruce Hart
> 1976 Palm Beach
> Milliken, Co
> GMC=Got More Class
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>