Home » Public Forums » GMCnet » Alternator Failure
| Alternator Failure [message #345077] |
Wed, 10 July 2019 07:31  |
Bruce Hart
Messages: 1501
Registered: October 2011
Location: La Grange, Wyoming
Karma: 5
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Senior Member |
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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
1977 28' Kingsley
La Grange, Wyoming
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| Re: Alternator Failure [message #345078 is a reply to message #345077] |
Wed, 10 July 2019 08:05  |
jhbridges
Messages: 8412
Registered: May 2011
Location: Braselton ga
Karma: -74
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Senior Member |
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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
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| Re: Alternator Failure [message #345095 is a reply to message #345077] |
Wed, 10 July 2019 12:46 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
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Senior Member |
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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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| Re: Alternator Failure [message #345103 is a reply to message #345077] |
Wed, 10 July 2019 15:35 |
jhbridges
Messages: 8412
Registered: May 2011
Location: Braselton ga
Karma: -74
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Senior Member |
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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
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| Re: Alternator Failure [message #345112 is a reply to message #345103] |
Wed, 10 July 2019 20:25 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Senior Member |
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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
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| Re: [GMCnet] Alternator Failure [message #345114 is a reply to message #345112] |
Wed, 10 July 2019 21:13 |
Bruce Hart
Messages: 1501
Registered: October 2011
Location: La Grange, Wyoming
Karma: 5
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Senior Member |
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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 <
gmclist@list.gmcnet.org> wrote:
> 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
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Bruce Hart
1976 Palm Beach
1977 28' Kingsley
La Grange, Wyoming
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| Re: [GMCnet] Alternator Failure [message #345117 is a reply to message #345114] |
Thu, 11 July 2019 00:26 |
jimk
Messages: 6734
Registered: July 2006
Location: Belmont, CA
Karma: 9
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Senior Member |
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https://www.gmcrvparts.com/product-p/gm7-028.1.htm
On Wed, Jul 10, 2019 at 7:14 PM Bruce Hart via Gmclist <
gmclist@list.gmcnet.org> wrote:
> 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 gmclist@list.gmcnet.org> wrote:
>
>> 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@appliedairfilters.com
http://www.appliedgmc.com
1-800-752-7502
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Unsubscribe or Change List Options:
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Jim Kanomata
Applied/GMC
jimk@appliedairfilters.com
www.appliedgmc.com
1-800-752-7502
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| Re: [GMCnet] Alternator Failure [message #345152 is a reply to message #345117] |
Thu, 11 July 2019 20:30 |
Bruce Hart
Messages: 1501
Registered: October 2011
Location: La Grange, Wyoming
Karma: 5
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Senior Member |
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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 <
gmclist@list.gmcnet.org> wrote:
> https://www.gmcrvparts.com/product-p/gm7-028.1.htm
>
> On Wed, Jul 10, 2019 at 7:14 PM Bruce Hart via Gmclist gmclist@list.gmcnet.org> wrote:
>
>> 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 > gmclist@list.gmcnet.org> wrote:
>>
>>> 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@appliedairfilters.com
> 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:
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Bruce Hart
1976 Palm Beach
1977 28' Kingsley
La Grange, Wyoming
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| Re: [GMCnet] Alternator Failure [message #345156 is a reply to message #345152] |
Thu, 11 July 2019 22:52 |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
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Senior Member |
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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 <
gmclist@list.gmcnet.org> wrote:
> 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 gmclist@list.gmcnet.org> wrote:
>
>> https://www.gmcrvparts.com/product-p/gm7-028.1.htm
>>
>> On Wed, Jul 10, 2019 at 7:14 PM Bruce Hart via Gmclist > gmclist@list.gmcnet.org> wrote:
>>
>>> 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 >> gmclist@list.gmcnet.org> wrote:
>>>
>>>> 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@appliedairfilters.com
>> 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
>
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Ken Henderson
Americus, GA
www.gmcwipersetc.com
Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
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| Re: [GMCnet] Bruce's Alternator Failure [message #345201 is a reply to message #345114] |
Fri, 12 July 2019 19:58 |
Emery Stora
Messages: 959
Registered: January 2011
Karma: 4
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Senior Member |
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The final story on this is that we worked on it a couple of hours and traced wires and checked isolator and found that there was 12 volts on the nichrome exciter wire to the alternator.
But it still wouldn’t start. It sure seemed like an open wire somewhere.
Bruce finally opened the alternator on the bench and checked all wires and connections and brushes.
He put it back together and installed it and it is now producing over 14 volts.
Probably a bad internal connection or a stuck brush.
Emery Stora
77 Kingsley
Frederick, CO
> On Jul 10, 2019, at 8:13 PM, Bruce Hart via Gmclist wrote:
>
> 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 gmclist@list.gmcnet.org> wrote:
>
>> 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
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| Re: [GMCnet] Bruce's Alternator Failure [message #347659 is a reply to message #345201] |
Wed, 11 September 2019 05:26 |
Bruce Hart
Messages: 1501
Registered: October 2011
Location: La Grange, Wyoming
Karma: 5
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Senior Member |
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Took motor home for a drive and the alternator failed again. Check contact connection on back side of fuse holder-all was good. Ran a second exciter wire with a 10watt 10 ohm resister still nothing.
Took a break from the alternator problem for a few weeks. Had lunch with Larry C. and told him of the problem I was having. He called me later and we went through the schematic of the alternator wiring and kept questioning why I have exciter voltage with key on but it drops out when the engine starts. Next day I went down to the Motorhome and just started poking around and saw an itsy bitsy spring under the accelerator pedal (ignition switch). Replaced ignition switch and alternator charging again. When, where, and why that spring came loose I will never know.
I want to thank everyone for their input and help with my alternator problem.
This is the second time I have posted this update but never saw it posted.
Bruce Hart
1976 Palm Beach
1977 28' Kingsley
La Grange, Wyoming
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| Re: Alternator Failure [message #347669 is a reply to message #345077] |
Wed, 11 September 2019 10:00 |
jhbridges
Messages: 8412
Registered: May 2011
Location: Braselton ga
Karma: -74
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Senior Member |
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Thanks for the followup! If nobody puts up what cures the weird ones, the exercise is repeated every time it happens to somebody. Busted switch never crossed my mind. Or presumably anybody else's either.
--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
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