House Battery connection clean up

T

tom geiger

New member
Dec 31, 2006
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So after getting all the front battery connections cleaned up I went back to the house battery connections to clean those up and got a spark from the
first connection I tried to unbolt. This was with no house battery and the coach unplugged. Do I remember correctly that the isolator is suppose to
separate the starter battery from the house battery? The starter battery is the only thing ghat has current to spark like that. Has my isolator
failed?

Thanks,
TG
76 Eleganza 2
KCMO
 
Tom,

You're absolutely correct that the isolator should prevent the
chassis/starter battery from feeding the house battery. But it's not
likely that the voltage you saw at the house battery terminal came from the
chassis battery because the common failure mode of the isolator is to
become OPEN, not shorted. It's much more likely that some wire has been
misconnected, less likely that the solenoid relay for the boost function
(below the isolator on the firewall) has "welded" closed, and somewhat more
likely that the dash Boost switch is ON ('tho' your '76 Eleganza should
have a momentary switch there).

Use a trouble light to easily track down the problem.

Ken H.

On Fri, Jul 17, 2020 at 1:25 PM tom geiger via Gmclist <

> So after getting all the front battery connections cleaned up I went back
> to the house battery connections to clean those up and got a spark from the
> first connection I tried to unbolt. This was with no house battery and the
> coach unplugged. Do I remember correctly that the isolator is suppose to
> separate the starter battery from the house battery? The starter battery
> is the only thing ghat has current to spark like that. Has my isolator
> failed?
>
> Thanks,
> TG
> 76 Eleganza 2
> KCMO
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
 
I was just trying to take apart the cables and wires off one of the relays back there to clean up the connectors with a brass brush. Just wasn’t
expecting sparks back there when everything is disconnected except for the starter battery, which I thought was separated from the wiring back at the
house.

TG
 
Whoa now! I hadn't read this "...back there..." statement before my
previous email. If you were working in the rear of the coach, you were
working with connections to the house battery, which I understood to still
be connected. I, too, am confused.

Ken H.

On Fri, Jul 17, 2020 at 2:19 PM tom geiger via Gmclist <

> I was just trying to take apart the cables and wires off one of the relays
> back there to clean up the connectors with a brass brush. Just wasn’t
> expecting sparks back there when everything is disconnected except for the
> starter battery, which I thought was separated from the wiring back at the
> house.
>
> TG
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
 
You are likely seeing a spark from the filter capacitors in the power converter and/or inverter (if you have one). What I can't figure out is you say
you have no House battery and not plugged in.

So... either your isolator has both internal diodes shorted... or the Batt Boost switch is stuck ON (You have a 1976 so it should be spring loaded)...
or get out your Voltmeter and trace down where the power is coming from.
--
Bruce Hislop
ON Canada
77PB, 455 Dick P. rebuilt, DynamicEFI EBL EFI & ESC.1 ton front end
http://www.gmcmhphotos.com/photos/showphoto.php?photo=29001
My Staff says I never listen to them, or something like that
 
> So after getting all the front battery connections cleaned up I went back to the house battery connections to clean those up and got a spark from
> the first connection I tried to unbolt. This was with no house battery and the coach unplugged. Do I remember correctly that the isolator is
> suppose to separate the starter battery from the house battery? The starter battery is the only thing ghat has current to spark like that. Has my
> isolator failed?
>
> Thanks,
> TG
> 76 Eleganza 2
> KCMO

Do you happen to have a solar panel by any chance?

--
Tom Lins
St Augustine, FL
77 GM Rear Twin, Dry Bath, 455, Aluminum Radiator Quad-Bag Suspension Solar Panel
Manuals on DVD
GMC Dealer Training Tapes
http://www.bdub.net/tomlins/
 
No solar panel . I’ve been searching on the web for a battery cable, starter and house battery cable hookup diagram for up front. Something that
would show how the battery cables are suppose to be arranged. Have not found anything as of yet. The electrical diagrams I have out of my manuals
don’t show the isolator in the diagram, so I’m not see a clear correlation with them.

I’ll try to describe my arrangement to verify I have them connected correctly. The positive battery cable goes up to the positive juntion post on
the aluminum plate. I have a short positive cable going from that junction down to the silinoid right side post. On that right side post I also have
another battery cable that goes down to the starter. The left side solenoid post has the house battery cable connected to it. The last negative
battery cable goes down and grounds on the engine block. Thats the main battery cable arrangement.

Thanks,
TG
 
> No solar panel . I’ve been searching on the web for a battery cable, starter and house battery cable hookup diagram for up front. Something
> that would show how the battery cables are suppose to be arranged. Have not found anything as of yet. The electrical diagrams I have out of my
> manuals don’t show the isolator in the diagram, so I’m not see a clear correlation with them.

I am looking at two different versions of the standard GMC wiring diagrams and the isolator is definitely there. It is labeled "Generator Output
Diodes" Look down the left side of the diagram not too far from the top and you will see the words "Generator Output Diodes". The isolator outputs
go to the boost relay called the "Auxiliary Battery Switch" and the "Battery Pickup Junction Block".

The other items you asked for are also shown on the diagram. If you do not have the GMC wiring diagram, download it from www.bdub.net or buy a huge
one on paper from Ken Henderson. His son Alan prints them.

--
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
 
One more item I had forgotten anout was the internal living area lights worked even when the house battery was out so the starter battery is somehow
feeding those circuits.

TG
 
Do you have a generator battery back there that someone might have tied
into?

Sully
Bellevue wa

On Sat, Jul 18, 2020 at 1:52 PM tom geiger via Gmclist <

> One more item I had forgotten anout was the internal living area lights
> worked even when the house battery was out so the starter battery is somehow
> feeding those circuits.
>
> TG
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
 
So looking at the wiring diagram it shows starter, pos battery and a short pos jump #4 cables all going to the right post of the Aux Battery Sw which
is mounted on the aluminum plate/fire wall by the isolator. The post length there seems to be too short to tie all 3 cables on it.
 
Tom,

Have you checked that non-original isolator for correct connections and
functioning? It's got 'way more terminals than I've ever seen on one.

Ken H.

On Sat, Jul 18, 2020 at 5:41 PM tom geiger via Gmclist <

> So looking at the wiring diagram it shows starter, pos battery and a short
> pos jump #4 cables all going to the right post of the Aux Battery Sw which
> is mounted on the aluminum plate/fire wall by the isolator. The post
> length there seems to be too short to tie all 3 cables on it.
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
 
Hard to tell being no where near the coach, but perhaps PO stacked all the cables on one side of the boost solenoid as a “temporary” fix for no
house battery.
--
John Lebetski
Woodstock, IL
77 Eleganza II
 
Yes electrical is always fun to figure out. I think I’ll try to find the flat connectors instead of the thinker battery connectors you get when you
get a battery cable.
 
Ken, I’ll check the isolator and more like just replace it with new one. I do have a combiner around here in its package, never installed it. May
be time to here.

TG
 
Tom,

At this point you should be aware that with the house lights on the main engine battery, you are all set up for a "Totally Dead Coach" syndrome. It
is important that this situation be corrected.

With the expertise you have on tap here (not to include yours truly), this should not be that difficult to get squared away.

Now, please do both us and you a favor. Create a sigfile. To do this go up to then down to and click.
There will be a box - Signature - in that box put something like:
Tom Geiger, 76 Eleganza 2, KCMO

We like to know who it is we are helping and be able to know you when we meet at a rally. The 76 Eleganza 2 is essential because not all coaches
are/were the same and this save me having to go back to you lead post all the time. And KCMO is so if there is someone that can assist that is in
striking range, he can contact you. (This last actually happens a lot here.)

Now, something read like you have wiring diagrams. If you don't we can fix that. I will add to the suggestion that you compare what is under the
right hood and see if you can spot a mis-placed connection.

Hang in there this group has gotten more and bigger problems than this fixed.

Matt
--
Matt & Mary Colie - '73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan
OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Twixt A2 and Detroit
 
Thanks Matt, appreciate the help. As I mentioned before not real knowledgeable on electrical stuff but am doggedly stubborn in trying to fixing
something thats not correct on it. This apparent current draw from the starter battery points to me on the isolator but did not consider the booster
switch although its a 76 so booster switch springs back to the off position. The starter battery feeding the interior lights has been something
I’ve notice this season.

TG
--
Tom Geiger
76 Eleganza II
KCMO
 
It appears the isolator may have given it up. Got a new one ordered and its on its way.

Fingers crossed,
TG
--
Tom Geiger
76 Eleganza II
KCMO
 
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