[GMCnet] Battery Selector (boost) Switch -- 73,74,??

[Mr.erf ERFisher]

Well so that we have something to talk about, ever wonder why your 73/74
battery boost switch would not work when the engine battery is discharged (
just when you need to boost) this will show you what is going on.

The boost switch on the 73/74 (and maybe more years) GMCs has several
problems:
1 is not momentary so it will lock on and parallel both battery banks
2 not key-switched, so if accidentally left on, it will draw power and run
down both battery banks
3 will not operate with the engine battery dead
4 provides power for the dash radio ( the silent killer of the engine
battery)

Here is an easy fix for;
1 boost relay only with the key on in the ign (engine run) mode
2 boost relay from the engine battery
3 dash radio only in the ign position.

This modification requires no rewiring, or modifications. Just remove a
fuse and add a jumper. Also shown in this presentation is the email from
JimB proposing these sort of modifications.

The next phase of this work, will make the switch momentary, and power the
boost relay from both batteries like is done on the 75- models.
So if you want these features, stay tuned and it will be coming soon with
more extensive modifications.

gene

--
Gene Fisher -- 74-23,77PB/ore/ca
"Give a man a fish; you have fed him for today --- give him a URL and
-------
http://gmcmotorhome.info/
Alternator Protection Cable
http://gmcmotorhome.info/APC.html
_______________________________________________
GMCnet mailing list
Gmc...@temp.gmcnet.org
http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist

[Dan Gregg]

Bring it on....
Dan
--
Dan & Teri Gregg

http://www.danandteri.blogspot.com

Halon Automatic Fire Extinguishers,
Rebuilt Fuel Sending Units

[Mr.erf ERFisher]

your tag line does not say what year your coach is

does your boost switch lock on?
gene

--

Gene Fisher -- 74-23,77PB/ore/ca
"Give a man a fish; you have fed him for today --- give him a URL and
-------
http://gmcmotorhome.info/
Alternator Protection Cable
http://gmcmotorhome.info/APC.html

[Carleton Douglas]

Gene, I have a 73/26,

Thanks

--
Carleton Douglas
73 custom, by myself
Prescott, AZ

[Mr.erf ERFisher]

Dang
all that work and I forgot the link
http://www.gmcmhphotos.com/photos/showphoto.php?photo=27964

arg
gene

[Dan Gregg]

[quote title=Mr ERFisher wrote on Sat, 13 December 2008 15:29]your tag line does not say what year your coach is I fixed that.

does your boost switch lock on? Nope
gene

--
Dan & Teri Gregg

74 Glacier

[Tom Fort]

Gene,
Are the photos in the correct order? Seems like it might be out of sequence:
1. 73-74 Boost Switch Mod
2. 73/74 Boost Switches (JimB email)
3. 73/74 Boost Switch Wiring
4. Remove Fuse and add a Jumper (behind glove box)
5. 75-78 Boost Switch Wiring

If this is the correct order, I want the simplest method. Which pictures should I use?
Thanks,
Tom

--
Tom Fort, KA4KGR
73 Painted Desert, Family owned Since 1973
Lugoff, SC

[Mr.erf ERFisher]

yes the order is correct

#4 is the one that shows how to add the jumper for the results.

the other slides show the way the switch is wired not old boost switch and
the 75 and newer boost switches.

gene

--

Gene Fisher -- 74-23,77PB/ore/ca
"Give a man a fish; you have fed him for today --- give him a URL and
-------
http://gmcmotorhome.info/
Alternator Protection Cable
http://gmcmotorhome.info/APC.html

[Mr.erf ERFisher]

spelling

On Sat, Dec 13, 2008 at 6:08 PM, Mr.erf ERFisher <mr.er...@gmail.com>wrote:

> yes the order is correct
>
> #4 is the one that shows how to add the jumper for the results.
>

> the other slides show the way the switch is wired now, old boost switch

[James Thompson]

I have a 75 Avion and my boost switch is not a momentary. What TZE number did GMC change to the momentary. How can I tell if it is wired like a 74 or a 75?

Jim T 75 Avion GA.

[Steven Ferguson]

Gene,
The boost switch in my EII is momentary.

--
Steve Ferguson
'76 EII
Sierra Vista, AZ
Urethane bushing source
www.bdub.net/ferguson/

[Mr.erf ERFisher]

It looks like it did not go by year, some transmodes went up to at least 75

so the easy way to tell is look at the back of the boost switch, I showed a
picture that will let you see if it has wires off one side of the switch or
both sides.

gene

On Sun, Dec 14, 2008 at 3:02 AM, James Thompson
<tjames...@bellsouth.net>wrote:

--

Gene Fisher -- 74-23,77PB/ore/ca
"Give a man a fish; you have fed him for today --- give him a URL and
-------
http://gmcmotorhome.info/
Alternator Protection Cable
http://gmcmotorhome.info/APC.html

[Mr.erf ERFisher]

need to find a way to get the wiring diagrams straight for the transmodes.
Seems like they were different clear up to 75

gene

[Mr.erf ERFisher]

rethinking your question:

The best way to see if you have the old or the new wiring is:

1 remove the fuse shown on slide #4 (labeled AUX BAT)

2 if your boost switch still works - you have the new wiring and you will
have to make your switch a momentary switch. ( I hope someone one has
pictures of doing this )

3 if your boost switch does not, put in the jumper and now the boost switch
works with the ignition key ;>)

gene

[Ken Henderson]

Make that at least to '76 TZE...1080 for my Birchaven with latching
boost switch.

Ken Henderson
Americus, GA
www.gmcwipersetc.com
'76 X-Birchaven

Mr.erf ERFisher wrote:
> need to find a way to get the wiring diagrams straight for the transmodes.
> Seems like they were different clear up to 75
>
> gene
>
>
>

[Mr.erf ERFisher]

that's kewl

so I have to change all of my titles, from73/74 - old-new , etc

but , I have added two new slides that show the fuse blocks (old-new wiring)
http://www.gmcmhphotos.com/photos/showphoto.php?photo=27978

so maybe you can tell me which fuse block your 76 has ?

and if the rest of you do not have a momentary switch, tell me which fuse
block you have. ( no dash panels to remove ;>)

in fact, I would like to id the mods by the fuse block if possible

good morning to you Ken and Steve
gene

--

Gene Fisher -- 74-23,77PB/ore/ca
"Give a man a fish; you have fed him for today --- give him a URL and
-------
http://gmcmotorhome.info/
Alternator Protection Cable
http://gmcmotorhome.info/APC.html

[David L Greenberg]

On Sun, 14 Dec 2008 05:02:36 -0600 James Thompson
<tjames...@bellsouth.net> writes:
>
>
> I have a 75 Avion and my boost switch is not a momentary. What TZE
> number did GMC change to the momentary. How can I tell if it is
> wired like a 74 or a 75?
>
> Jim T 75 Avion GA.
> _______________________________________________

Transmodes generally didn't get the 75-78 upgrades and mods.

David Lee Greenberg
Port St Lucie, FL
Dedicated to the Preservation of the Classic GMC Motorhome
www.gmcss.com/Registry.htm
http://gmcmhregistry.com/

____________________________________________________________
Save $15 on Flowers and Gifts from FTD!
Shop now at http://offers.juno.com/TGL1141/?u=http://www.ftd.com/17007

[Mr.erf ERFisher]

so will be interesting to see if they got the new wiring or kept the old

gene

On Sun, Dec 14, 2008 at 6:47 AM, David L Greenberg
<davegre...@juno.com>wrote:

--

Gene Fisher -- 74-23,77PB/ore/ca
"Give a man a fish; you have fed him for today --- give him a URL and
-------
http://gmcmotorhome.info/
Alternator Protection Cable
http://gmcmotorhome.info/APC.html

[Guy Lopes]

I changed the title, so I hope that I have started a new thread and I'm not
hijacking the original thread.

What timely information! I have a 75 Avion that I bought in late Sept. I
visit her in the storage facility regularly and have been performing light
maintenance and housekeeping. I usually start her every few weeks and let
the oil, transmission fluid and APU completely warm up and stabilize during
my visit.

A couple of weeks ago I attempted to start her and the battery was dead.
Yes, the boost switch had been left in the Boost position from my previous
visit so all batteries were dead. Lesson learned.

I attempted to jump the coach battery with the boost switch off. It appeared
to work but didn't quite have enough juice to turn the engine over. As I
approached the front of the GMC from the outside I was surprised to find a
tremendous amount of smoke coming from the engine compartment. I don't even
remember disconnecting the jumper cables - it happened so fast!

When the smoke cleared I found two fairly heavy gauge wires fried.

A picture of the mess is here:
http://guylopes.startlogic.com//Pics/burntwires1.jpg

My hunch is that the boost solenoid failed in the closed position, then when
I attempted to jump start, the current was too much for the smaller wires to
handle and this is what caused the smoke to try to escape the system.

Any opinions or advice? Thank you in advance.

Merry Christmas to all,

Guy
Sacramento, CA

'75 Avion
www.737guy.com

[Jim Kanomata]

Guy,
Your not the first to do that. I did that many years ago before I took the
time to fingur it out.
Always use the positive jumper cable to the nut marked for that use.

--
Jim Kanomata
Applied/GMC, Fremont,CA
ji...@appliedairfilters.com
http://www.appliedgmc.com
1-800-752-7502

[Guy Lopes]

Jim,

Thanks for the response. So you don't think that my solenoid failed, I just
jumped it incorrectly?

Guy

-----Original Message-----
From: gmclist...@temp.gmcnet.org
[mailto:gmclist...@temp.gmcnet.org] On Behalf Of Jim Kanomata
Sent: Sunday, December 14, 2008 9:04 AM
To: gmc...@temp.gmcnet.org
Subject: Re: [GMCnet] Problem With Battery Selector (boost) Switch - ?

Guy,
Your not the first to do that. I did that many years ago before I took the
time to fingur it out.
Always use the positive jumper cable to the nut marked for that use.

On Sun, Dec 14, 2008 at 8:43 AM, Guy Lopes <guyl...@surewest.net> wrote:

> I changed the title, so I hope that I have started a new thread and I'm
not
> hijacking the original thread.
>
> What timely information! I have a 75 Avion that I bought in late Sept. I
> visit her in the storage facility regularly and have been performing light
> maintenance and housekeeping. I usually start her every few weeks and let
> the oil, transmission fluid and APU completely warm up and stabilize
during
> my visit.
>
> A couple of weeks ago I attempted to start her and the battery was dead.
>

<snipped>

[RJW]

> What timely information! I have a 75 Avion that I bought in late Sept. I
> visit her in the storage facility regularly and have been performing light
> maintenance and housekeeping. I usually start her every few weeks and let
> the oil, transmission fluid and APU completely warm up and stabilize
during
> my visit.

You may find that the current conventional wisdom is to not start her up
unless you are going to run it on the road and really get everything hot. I
used to do what you do and both of my mufflers rusted out. You simply can't
get everything hot enough to get rid of water vapor while running parked.
Exercising the generator is probably OK while parked.

Richard
SE Michigan
Website: www.PalmBeachGMC.com

[John Wright]

Guy,
Running your engine every few weeks does not help in its longevity.
Dick Paterson (the engine guru) says you do more harm than good as
the oil never get to operating temp with the engine idling, it take
15 to 20 minutes going down the read to get the oil up to temp and
drive off the condensation. If the engine oil was change along with
the filter you can store the engine 3 to 6 months without issue.
This is one myth that is bad for our engines. Where you live the
temperature does not get quite as cold as it does here for the winter
months but the same rule applies. I also have a 75 Avion that is
under going a frame up restoration.
J.R. Wright
GMC GreatLaker
77 Eleganza Custom
1975 Avion Under Reconstruction
Michigan

[Mr.erf ERFisher]

I am not sure what happened , but the good news is the wire burned up was
put there by the PO going to a current shunt for an ammeter somewhere. It
goes from the isolator to the shunt , to the battery stud on the firewall.
You can easly replace this wire, It was too small from the look of it and
you were prob trying to crank through this wire (300 amps or so)

when you jump, I would recommend to put the jump wires directly on the
engine battery so the current comes from the correct place.

looks like no harm done ( maybe the isolator)

gene

On Sun, Dec 14, 2008 at 8:43 AM, Guy Lopes <guyl...@surewest.net> wrote:

--

Gene Fisher -- 74-23,77PB/ore/ca
"Give a man a fish; you have fed him for today --- give him a URL and
-------
http://gmcmotorhome.info/
Alternator Protection Cable
http://gmcmotorhome.info/APC.html

[Mr.erf ERFisher]

>
>

so the burning question is JR, do you have a momentary boost switch and
which fuse block do you have ?

gene

> I also have a 75 Avion that is
> under going a frame up restoration.
> J.R. Wright
>

>

> --
> Gene Fisher -- 74-23,77PB/ore/ca
> "Give a man a fish; you have fed him for today --- give him a URL and
> -------
> http://gmcmotorhome.info/
> Alternator Protection Cable
> http://gmcmotorhome.info/APC.html
>

[Ken Henderson]

Guy,

I agree with Gene that the device on the heater box is probably the
current shunt for an added ammeter -- the unburned red wires attached to
each end of it should go to the ammeter in the cockpit. But I disagree
with him about how much current it might normally carry. The burned
wire should never see more than the alternator charging current, 60=100
amps, for which it might have been adequate. But that was not a good
location for the shunt either, because it would read only charge
current, never discharge current.

The question is, what happened? Unless the isolator is bad, no current
should have flowed through the wire between the isolator and the
firewall positive connection unless you put the positive jumper to the
isolator. I can't figure out any other way for that wire to be called
on for that much current. Is that what you did?

I see nothing to indicate that there's anything wrong with your boost
solenoid nor that it had anything to do with the scorched wires.

Safest procedure is to always connect the positive charger/boost battery
terminal to the dead battery's positive terminal. Then connect the
negative helper terminal to the grounded end of the dead battery's
negative cable == or nearby.

Ken Henderson
Americus, GA
www.gmcwipersetc.com
'76 X-Birchaven

[Gordon]

Folks;
Please read this carefully and keep your face out of the battery
compartment looking for the negative battery terminal to connect to.
Do as Ken says;

"Safest procedure is to always connect the positive charger/boost battery

> terminal to the dead battery's positive terminal, (FIRST). Then
connect the negative helper terminal to the GROUNDED END of the dead
battery's
> negative cable == OR NEARBY." DO NOT CONNECT TO THE NEGATIVE
TERMINAL OF THE BATTERY.
Those who have seen a battery explode will understand better than those
who have been lucky so far.
Ken;
My boost switch seems to be upside down. I think the Boost is on when
the top is pushed in and off when the bottom is pushed in. 1973, not
spring loaded.
Gordon

[Guy Lopes]

Thank you all for the replies.

When I jumped the GMC I attached the cables directly to the dead battery's
posts. I normally would have attached the neg cable to a nearby ground, but
there was nothing nearby.

I do like having an ammeter, along with a voltmeter, to be able to determine
the condition of the battery and charging system.

The more that I dig into my pride and joy, the more I scratch my head about
some of the things that I am finding from the PO. They took great care of it
but some of the wiring is questionable. As an example, they installed a home
style burglar alarm in the coach (which doesn't appear to have worked for a
long time), and much of the wiring is 2 conductor home electrical wire...

...and now the shunt.

I enjoy the journey though and am having a blast with my GMC!

I should have elaborated a bit in my original post regarding the running of
the engine, etc. I don't simply let it idle in its parking spot to warm up.
I usually drive it out of the lot, through town at 25 mph for a couple of
miles, then up to 50 mph when I get outside of town. I tell my wife that I
have to keep her running and all systems working, but truth be told I simply
enjoy driving her. Plus it knocks all of the cob webs off!

I have many things to do this winter and will be ordering parts from both
Jims. I'm planning on a new paint job in the spring or summer.

Guy
Sacramento, CA

'75 Avion
www.737guy.com

-----Original Message-----
From: gmclist...@temp.gmcnet.org
[mailto:gmclist...@temp.gmcnet.org] On Behalf Of Ken Henderson
Sent: Sunday, December 14, 2008 10:54 AM
To: gmc...@temp.gmcnet.org
Subject: Re: [GMCnet] Problem With Battery Selector (boost) Switch - ?

Guy,

<snipped>

[Ken Henderson]

Guy,

Please let us know how you managed to run a couple of hundred amps
through that wire. :-)

Ken Henderson
Americus, GA
www.gmcwipersetc.com
'76 X-Birchaven

Guy Lopes wrote:
> Thank you all for the replies.
>
> When I jumped the GMC I attached the cables directly to the dead battery's
> posts. I normally would have attached the neg cable to a nearby ground, but
> there was nothing nearby.
>
> I do like having an ammeter, along with a voltmeter, to be able to determine

> the condition of the battery and charging system...

[Ken Henderson]

Easy enough to check with a test light at the solenoid. Unfortunately,
those switches are mounted with screws into ears top & bottom so the
bezel has to come off to invert them. It may be that the connector is
symmetrical so you can just invert it from behind the dash -- but I
doubt it. :-(

Ken H.

Gordon wrote:
> ...My boost switch seems to be upside down. I think the Boost is on when

> the top is pushed in and off when the bottom is pushed in. 1973, not
> spring loaded.

[Mr.erf ERFisher]

If you pull the fuse in slide 4 the boost relay will go off. You should be
able to hear if the switch is on

gene

My boost switch seems to be upside down. I think the Boost is on when
> the top is pushed in and off when the bottom is pushed in. 1973, not
> spring loaded.
> Gordon
>

> --
> Gene Fisher -- 74-23,77PB/ore/ca
> "Give a man a fish; you have fed him for today --- give him a URL and
> -------
> http://gmcmotorhome.info/
> Alternator Protection Cable
> http://gmcmotorhome.info/APC.html

[Gordon]

Thanks for the suggestions. My problem is a foot of snow and the
motivation to get off the couch. I have blown the driveway clear, but
will have fun getting into the coach.
Gordon

[Randy]

Wouldn't you want the boost solenoid powered by the house battery, which you are assuming is good and are planning to use to start the engine? Powering the solenoid through the engine battery would be useful is you were planning on charging the house battery as you travel down the road (something that can be accomplished by the genset as well, no?)

Unless I'm missing something here.
--
Randy
1973 26' Painted Desert
Ahwatukee (Phoenix) AZ

[Gordon]

Randy;
I think you are correct and the system can be improved by wiring it in
than manner. The original assumption have been that you run the house
battery down while camping and it normally ends up lower in voltage than
the engine battery.
Gordon

Randy wrote:
>
>
> Wouldn't you want the boost solenoid powered by the house battery,
> which you are assuming is good and are planning to use to start the
> engine? Powering the solenoid through the engine battery would be
> useful is you were planning on charging the house battery as you
> travel down the road (something that can be accomplished by the
> genset as well, no?)
>
> Unless I'm missing something here.

[Mr.erf ERFisher]

this is true and you can see by the slides the new wiring does just that.
However, you still need a momentary switch.

The voltage source that turns on with the key protects you if you forget the
boost switch and you run down all the batteries. this is what the jumper
does with no wiring mods

so

the simple thing to do is the jumper mod I showed, so that if you want to
lock on the boost switch you can do it while the key is on.

You will see at the bottom of the slide (#4), I said you could connect to a
house battery but, I would suggest a voltage source that is controlled by
the key.

the momentary switch makes it OK to use both batteries to switch the boost
relay, because you cannot lock it on. So the next part of the project is to
provide the momentary function without tearing up the dash to modify the
switch.

gene

--

Gene Fisher -- 74-23,77PB/ore/ca
"Give a man a fish; you have fed him for today --- give him a URL and
-------
http://gmcmotorhome.info/
Alternator Protection Cable
http://gmcmotorhome.info/APC.html

[John Shotwell]

Mr ERFisher wrote on Sun, 14 December 2008 07&#58;15

> need to find a way to get the wiring diagrams straight for the transmodes.
> Seems like they were different clear up to 75
>
> gene

Gene, our '78 Royale (transmode) is not momentary.

John
--
John Shotwell
Archbold, OH
78 Royale Center Kitchen

[Mr.erf ERFisher]

wow

I guess that is all transmodes.

which fuse block do you have

http://www.gmcmhphotos.com/photos/showphoto.php?photo=27978

gene

--

Gene Fisher -- 74-23,77PB/ore/ca
"Give a man a fish; you have fed him for today --- give him a URL and
-------
http://gmcmotorhome.info/
Alternator Protection Cable
http://gmcmotorhome.info/APC.html

[Guy Lopes]

Well Ken, that was the purpose of my email. I was hoping to get one of you
smart fellers to help me explain it. :-)

Guy

-----Original Message-----
From: gmclist...@temp.gmcnet.org
[mailto:gmclist...@temp.gmcnet.org] On Behalf Of Ken Henderson
Sent: Sunday, December 14, 2008 11:40 AM
To: gmc...@temp.gmcnet.org
Subject: Re: [GMCnet] Problem With Battery Selector (boost) Switch - ?

[Bob de Kruyff]

""Transmodes generally didn't get the 75-78 upgrades and mods.""

Now that's interesting! Have any more detail on what was and wasn't Dave? That would mean many of the Coachmans and such would have quite a few differences from GM finished coaches.

--
Bob de Kruyff
78 Eleganza
Chandler, AZ

[Charles Boyd]

Bob de Kruyff wrote on Mon, 15 December 2008 12&#58;02

> ""Transmodes generally didn't get the 75-78 upgrades and mods.""
>
> Now that's interesting! Have any more detail on what was and wasn't Dave? That would mean many of the Coachmans and such would have quite a few differences from GM finished coaches.

It seems all the transmodes used the 73-74 steering wheel.
--
C. Boyd
76 Crestmont by Midas
East Tennessee

[Charles Boyd]

C Boyd wrote on Mon, 15 December 2008 12&#58;18

> Bob de Kruyff wrote on Mon, 15 December 2008 12&#58;02
> > ""Transmodes generally didn't get the 75-78 upgrades and mods.""
> >
> > Now that's interesting! Have any more detail on what was and wasn't Dave? That would mean many of the Coachmans and such would have quite a few differences from GM finished coaches.
>
>
>
> It seems all the transmodes used the 73-74 steering wheel.

OOPS.. Seems in the brochure the 78 Coachman has the NEW style steering wheel but the 77 Birchaven does not??
http://www.bdub.net/publications/index.html

[Mike Miller]

My 78 Birch has the new style steering wheel. (TZE338v101163)
Not that I really like it...
--
Mike Miller
`73 26' X Painted D.
`78 23' Birchaven
Hillsboro, OR

[Bob de Kruyff]

""Transmodes generally didn't get the 75-78 upgrades and mods.""

I wonder if they were using excess old stock on Transmodes. I know that was always an issue with the car lines whether to scrap or turn excess year end stock into the service parts inventory.

--
Bob de Kruyff
78 Eleganza
Chandler, AZ

[David L Greenberg]

On Mon, 15 Dec 2008 11:47:49 -0600 Mike Miller <m00...@gmail.com>
writes:

>
>
> My 78 Birch has the new style steering wheel. (TZE338v101163)
> Not that I really like it...
> --
> Mike Miller
> `73 26' X Painted D.
> `78 23' Birchaven
> Hillsboro, OR
>

In 78 GM T&C was emptying the parts bins. The 78 GM finished coaches were
loaded with options and the Transmodes probably got some of the earlier
refinements. Just specualtion on my part. I was in the factory in 76 but
not 78.

David Lee Greenberg
Port St Lucie, FL
Dedicated to the Preservation of the Classic GMC Motorhome
www.gmcss.com/Registry.htm
M E R R Y C H R I S T M A S ! !
____________________________________________________________
Click here to find the satellite television package that meets your needs.
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[Rick Denney]

Mr.erf ERFisher writes...

> Here is an easy fix for;
> 1 boost relay only with the key on in the ign (engine run) mode
> 2 boost relay from the engine battery
> 3 dash radio only in the ign position.

Gene, seems to me that your item 2 is the same as the factory
arrangement--the boost relay is energized from the engine battery
already. I gather from below that you really intend to power the boost
solenoid from both batteries, and I think that's a good thing. It
should function no matter which battery is charged or discharged.

And I frequently listen to the radio when I'm working on the motorhome
with the ignition off. But I do have a (lighted) switch at the radio
that allows me to shut off power to it completely, and the radio I
bought lights the front panel when power is available, even when the
radio is in "standby" mode. That way, I don't forget.

Rick "not worried about the non-momentary switch" Denney

'73 230 Ex-Glacier "Jaws"
Northern Virginia

[Mr.erf ERFisher]

the latching switch is almost the whole point of this exercise because if it
is left on, it will (and does) run down both batteries.

the 73/74/ early transmodes did use only the engine battery but if you look
at the bottom of slide 4, it shows that you could remove the fuse, hook the
jumper to a fused house battery source, and you are good to go running the
boost from the house battery. you could also use two diodes to run from
both batterie sources , and then use the later technique
http://www.gmcmhphotos.com/photos/showphoto.php?photo=28164

of a second momentary switch to the boost relay to get the momentary
feature (that you are not worried about but most are) and not have to dig
behind the dash to change the wiring.

good luck
gene

>
>
> Rick "not worried about the non-momentary switch" Denney
>

> --
> Gene Fisher -- 74-23,77PB/ore/ca
> "Give a man a fish; you have fed him for today --- give him a URL and
> -------
> http://gmcmotorhome.info/
> Alternator Protection Cable
> http://gmcmotorhome.info/APC.html
>

[rwbmitiopt]

Guy
If this was on the negative side it would indicate a bad (open) ground on the battery. If you use that logic than whatever circuit (wire, switch, solenoid etc) is supposed to be carring the current is open thus routing the current through this small guage wire.
Rick D. where is your logical mind on this one? Guy just needs this problem solved not the issue the Thread Topic is directed at. LOL
Randy
SWA Guy wrote on Sun, 14 December 2008 19&#58;59

> Well Ken, that was the purpose of my email. I was hoping to get one of you

> smart fellers to help me explain it. :)
>
> Guy

>
>
>
>
> Subject: Re: [GMCnet] Problem With Battery Selector (boost) Switch - ?
>
> Guy,
>
> Please let us know how you managed to run a couple of hundred amps

> through that wire. :)
>
> Ken Henderson

--
Randy Burns
Mercer Is WA
75 EX GB

[Ken Henderson]

Guy,

This crudely modified wiring diagram of the isolator and area shows the
added ammeter and shunt in red:
http://www.gmcmhphotos.com/photos/showphoto.php?photo=28165

The wire in which the resistor (shunt) is shown is the one burned, as I
interpret your photos. Since the wires leading to the ammeter were not
damaged, we can rule out that circuit as a factor in the mishap.

Since no current can flow into the two outer terminals of a properly
operating isolator, connecting a positive booster to the Junction Block
end of the burned wire cannot have caused the problem.

Since the only current normally flowing into the center terminal of the
isolator is from the alternator, which was not operating, we can rule
out that as the cause of the problem.

The only option left is for the positive jumper to have been connected
to the isolator end of the burned red wire. Charging a battery via that
circuit probably would not have so seriously have damaged the wire;
attempting to start the engine with that wire supplying most of the
starter current COULD done so.

The only conclusion I can reach, from what I've seen, is that your
jumper was connected to the isolator at the red wire when you attempted
to start the engine.

Ken H.

Guy Lopes wrote:
> Well Ken, that was the purpose of my email. I was hoping to get one of you
> smart fellers to help me explain it. :-)
>
> Guy
>
>
>

> Please let us know how you managed to run a couple of hundred amps
> through that wire. :-)
>
>