Subject: Re: gmc: gmc motorhome Battery Cutout

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Date: Fri, 05 Dec 1997 09:53:10 -0500

From: Patrick Flowers

Subject: Re: GMC: GMC Motorhome Battery Cutout
john nepper, jr. wrote:


> I have a problem with the auxiliary battery in my '76 Palm Beach. It seems to drain itself after only a week or so... After several "dective" tries I've decided to just put a shutoff switch on the battery while it's in storage.


> Problem: The switch I bought says to install it on the negative side of the circut, is there any reason not to put it on the positive side?
You didn't say what type of switch it was, but many of these are a bare knife switch. By putting it on the negative side of the battery, if anything conductive touches the switch and gets grounded, it will not cause a problem. If the above occurs with the switch mounted on the positive side, the best outcome will be a nasty spark and an ensuing fire would be very likely.
Your problem is "parasitic" drain on the electric system. In the GMC's, this is usually a result of added "extras". Sound systems seem to be the worst culprits. You didn't outline what type of detective work you did, but the best approach is to turn everyting off and unplug everything you can from the 12V system. Next remove all the fuses(be sure to label each one or you'll have lots of fun getting them all back in the right slots) and disconnect the negative cables on both the motor and aux batteries. Connect an ammeter between the aux battery and negative cable. Hopefully, it will read zero. If not, then you probably have a short somewhere between the battery and the fuse panel (or someones tapped onto the cable before the fuse panel - it happens). Then insert and remove one fuse at a time noting which ones result in a reading on the ammeter. That will tell you which circuits are causing the problem. Once you know which circuit the culprit's on, you can disconnect the accessories on those circuits one at a time, noting the change in indication on the ammeter.
This is a long process and may be more trouble than it's worth since you've already decided to install the disconnect.
Hope this helps,

Date: Tue, 27 Jan 1998 08:07:35 -0500

From: Ralph Edelbach

Subject: GMC: Battery info?
Took the "new" '74 26 foot Glacier out for a short test run last Saturday, the sun was out for a while in NJ, and when it stalled at a stop sign, the battery could not spin the engine fast enough to get it restarted. Even with the switch in the "boost" position, it wasn't sufficient so a quick call to my wife who arrived and, after hooking up the jumper cables, the mighty 455 roared back into life. Time to replace one or more batteries I suppose.
My question pertains to whether it is necessary to replace both batteries up front with the same size ones or can I just buy a new engine battery? Like at least one other person, I haven't had a whole lot of luck following the electrical diagrams in the manuals yet but I intend to study them more. I have a lot of time since I'm still working and have not yet retired. The front battery tray was completely redone just before I bought the coach last week so everything appears to be in very good shape.
Any help will be greatly appreciated such as a good brand and size.

Happy motoring

Date: Tue, 27 Jan 1998 16:36:29 -0800

From: Phil Swanson

Subject: GMC: Battery Locations
Hello fellow GMCers,
With all this message traffic about batteries and locations, I decided to check out my newly acquired 1973 Canyon Lands closer with respect to batteries and cables. I have the two golf cart 6 Volt types in series in the front on the passenger side and one commercial battery back in the generator bay but I have no generator however. The battery in the back is functioning strictly for reserve capacity. One of the horrors I have however is the positive battery cable that runs underneath the coach on the left side to hook up the generator battery. As I inspected the insulation on the cable, I saw places that are chaffing on the frame and taped, but thankfully not worn through underneath. It would create one heck of a mess and/or fire if this cable decided to short out. Suggest if condition of cable is unknown, that you inspect the insulation and replace the cable or disconnect that back battery when not in use. I am going to invest in one of those little shut off switches at the battery post so I can electrically disconnect it and if and when I ever need it, I can tighten the green knob and restore a connection. I do not like the idea of this cable rubbing on sharp twists and bends in the frame. Maybe installing one of those outer jackets for wire looms often seen on custom installations, like on hot rods, would help. Anything to keep the cable from wearing through and creating a wild short. The bad thing about the stock configuration that I have is that is always live and a short waiting to happen. Maybe I will just get rid of the battery in the back since I have no generator. I could eventually get a Honda generator with rope start and get rid of the battery and the added weight in the rear where the GMCs are too heavy anyway and eliminate the possibility of catastrophic failure and possible loss of the coach.

Regards, Phil

Date: Mon, 26 Jan 1998 22:47:48 +0000

From: John Szalay

Subject: Re: GMC: RE: Battery locations
At 09:10 PM 1/26/98 +0000, you wrote:



>For whatever it's worth, I have a 78 Royale. Like you, I have two batteries on the right side of the engine compartment. However, my house battery is on the left side of the engine compartment.


> Paul Bartz


>> I've got a 1977 Royale with three batteries. Two 12 V batteries (starting and House) in the front engine compartment on a double battery tray and another 12 V battery in the Onan generator compartment for starting the generator.


>> I also have read that putting dissimiliar batteries in the same charging circuit will/can result in one of the batteries receiving insufficient charge.
That is true ONLY IF the batteries are connected in Parallel. If they are connected in series, its just as if they were one large battery. after all, your 12volt battery is a series of small cells connected in series to give you 12 volts.
>>it would seem I can't/shouldn't use the existing charging circuit, which now charges the two front batteries simultaneously, with a 12V battery on one terminal of the isolator and two 6v batteries on the other terminal.


yes you can.

+12- +6-+6-
The biggest problem is where to mount the large 6 volt batteries.
I also have 3 batteries in my 73, one for the engine, one for the house 12V

and one in the back for the Onan genset.


> ----------

> > From: Robert Dinsmore

> > To:

> > Subject: Re: GMC: RE: Battery locations

> > Date: Wednesday, January 28, 1998 3:20 AM

> >

> > John:

> >

> > I removed the grill and welded a battery tray to the crossmember directly in front of the radiator/air conditioning condenser. Then installed two Trojan 105 6 volt golf cart batteries in series rated at 200 amp hours. Reinstalled the grill with stainless steel wing nuts and lock washers so I could easily remove the grill for battery servicing.

> >

> > Battery cables were kept short to minimize voltage drop and for the most part all wiring to the inverter/charger is stock and left unchanged.

> >

> > Then I replaced the original 12 volt starting battery and house battery (located on the passenger side) with another two golf cart batteries that are used for only starting loads (1200 cold cranking amps that tell that 455 whose boss at 20 below zero in Wisconsin)

> >

> > The 6 KW Onan has a small starting battery adjacent to it so there is no reason for heavy battery cables strung the length of the motorhome.

> >

> > The advantage of the 4 golf cart battery system is: #1, I can squander my battery power, and listen to the radio any time I want without fear of discharging my starting battery... #2, In a pinch I can use the starting batteries to operate the load in the house (400 amps hours available to run my VCR/TV and space heater blowers in the winter). #3, As my house batteries die from hard deep cycling, I move the starting batteries into the house battery tray and buy new starting batteries. #4, I have TRUE DEEP CYCLE batteries designed to deliver 75 amps continously, not like most 8D truck batteries that are really just big starting batteries. #5, I have lots of redundancy. #5, Since I live on a boat in the summers and use the motorhome in the winter I do a lot of poor weather driving (22,000 miles in the last two years)... The extra weight up front comes in handy in the snow(about 280 pounds for 4 batteries).

> >

> > I notice no change in engine operating temperature, but I travel in the winter as far south as Arizona, Texas, and Georgia. My plan was to duct air from the grill opening to the radiator if I encounter an overheating problem, but so far I have not found it necessary.

> >

> > I use a like setup on my sailboat, (except I have 800 amp hours), and I cruise 5 months of the year in Alaska without electrical hookup during the entire time.

> >

> > Hope this helps

> >

> > Bob

Date: Wed, 28 Jan 1998 21:03:57 EST

From: (David L. Greenberg)

Subject: Re: GMC: Battery Locations

Watch out for those battery disconnects with the green knob. I installed one a couple of years ago and nothing but problems with it. It either didn't shut down all the way (One of the wags at the Carlysle show told me it allows a little voltage to creep thru to keep radio memorys working!) and sometimes it shut down when I would try to restart after getting fuel, etc.
I threw it away and installed a Knife Switch. It is much more positive and you can tell at a glance whether your batteries are in or out of the system.
Another approach is to use a rotary switch such as used on boats. In any event this works to have a theft deterrent function as well.


David Lee Greenberg

GMC Motorhome Registry

Date: Wed, 28 Jan 1998 21:03:57 EST

From: (David L. Greenberg)

Subject: GMC: Re: Battery locations
Your battery arrangements sound ideal.
One comment to add...I have installed my grill with 4 springs. They go back to the radiator frame and I can remove and replace the grill with out tools.
I like the idea of moving weight up front and I NEVER drive in snow!

David Lee Greenberg

Date: Fri, 30 Jan 1998 22:40:18 EST


Subject: Re: GMC: Re:GMC Re: Battery Locations
I'll add my two cents worth on auxillary battery position. I have a 77 Palm Beach. I did away with the battery in back and put two 6 volt golf cart batteries up front on the curb side. They are positioned one in front of the other with about an inch clearance at the closest point to the outside body. The engine battery is between them and the radiator shell. I used the same cable from the old battery position in the back to carry current from the golf cart batteries to the Onan. I have not had any problems. Since this is the vicinity the GM engineers chose for the engine battery, I assumed it would be better than trying to find another location. It is also closer to the electrical connections on the firewall.
As to additional weight and handling, I can't tell any difference. The batteries can be installed through the eyebrow opening.

Justin Hill

Date: Fri, 30 Jan 1998 22:17:28 -0800

From: Robert Dinsmore

Subject: Re: GMC: Re:GMC Re: Battery Locations
I fill my golf cart batteries 1/2 way between the lowest part of the fill tube and the plates. These batteries (Trojan 105) have a lot of water capacity above the plates. I have taken a 50 degree knock down with my sailboat and have not spilled a drop of battery acid).
These batteries are "not" maintenance free... you need to check the water level at a regular interval.
If it still bothers you, you can purchase special marine type battery caps that are designed to recover water that is boiled away during heavy recharge amps. Very expensive though.... so I ruled them out.

Philip L. Stewart wrote:


> I've read the discussions on installing auxillary batteries in the space behind the front grill and in front of the A/C condenser, radiator and in my case an auxillary transmission cooler coil. What's anybody's guess about the risk batteries in this location would pose to these parts due to the possibility of battery acid spills or corroisve

> venting from normal or accidental over-charging? I recently had to replace the radiator core on my coach and sure would hate to have to do that expensive job again. If this is a safe location otherwise, it seems

> like a good place to mount additional house batteries.

> Phil

Date: Sun, 8 Feb 1998 09:56:33 -0800

From: "Mike Finnicum"

Subject: Re: GMC: RE: Battery locations
Hi All,
Lots of activity while I was at our monthly GMC rally. So here is my 2 cents worth.
Re: Weight up front vs. batteries.

I have my original style battery in the back compartment. At the club we have about 150 members with 50-60 regularly showing up at the rallies. I have surveyed the group and about 20% have moved batteries forward (over 50% have switched to golf cart batteries). No one has yet moved them back. There are various reasons but storage (using old bat compartment for elec cords, hoses, oil, etc.) and weight up front appear the biggest.
Alex Sirum who owns a large GMC repair center in Ochachobee, FL say the weight is negligible compared to the total up front weight. He also says if you are wearing out bearings, check the hubs. If they are worn, bearings will wear out 2 to 5 times faster. You should NOT be able to turn the bearing inside the hub. The front axles are meant to carry 3500 lbs.. 75-100 lbs. of battery is only 2-3% of the total.
I am now planning to move mine up front at my next coach battery replacement.

Date: Tue, 17 Mar 1998 17:44:49 -0500

From: "John Massey"

Subject: GMC: Wiring for multiple batteries
Do I have a problem?
I've got three batteries in my 1977 Royale - Starting, House and Generator. The Maintenance manual diagrams, however, only show two. For example, the diagram entitled "1977 and 1978 GMC Motorhome Living Area 12-Voly DC Electrical System...." show how the "cranking" battery and "Aux" battery are connected. Part of my problem is that the House battery wire, that I would have expected to be routed back from the front, where the battery is located, to the converter in the rear, is not. Tracing the wire under the MH, the Red large gage wire is tied off in the vicinity of the generator and is terminated in a heavy ring terminal which is not connected to anything! Two inches away there is a Red wire from the generator battery and that is connected a stud terminal on what I believe to be a fuse (metal block about 2" by 3/4" with two studs). The other stud terminal is connected to a Black very large gage wire which goes to the converter. The "fuse" is just hanging in the air with the wires attached. So it looks like the way it is connected NOW, the generator battery is only charged by the converter and the house battery is only charged by the alternator. Also the Generator battery is the only source of 12 vdc for house needs.

If I were to connect the Red house battery wire to the same stud terminal that the Red generator wire is connected to, then, I think, I have the two batteries in parallel. Then both batteries would be charged by either the alternator when the engine is running or, when stationary, by the convertor when it gets shore power or AC from the generator. I am concerned that this would mean that, when the engine is running, the alternator would

be charging all three batteries - is this a problem?

This would also mean that when I select BATT BOOST, all three batteries are available for starting.

All three batteries are identical, looks as if they were bought at the same time about a year ago.

I just don't see a reason for someone disconnecting the House battery wire in the first place and am a bit apprehensive about reconnecting it. Hope this was clear enough.


FMCA 231235

Date: Wed, 18 Mar 1998 02:00:38 -0500

From: Bill Wallace

Subject: Re: GMC: Wiring for multiple batteries
John, I can help on this. My '78 Royale had same hookup. The "fuse" you describe is a circuit breaker to protect in case of a short in the wire to the front coach battery. The breaker on mine was wrapped in tape. Breaker was inoperative. Wire from gen and battery goes to one end of breaker. Wire from converter and wire from front coach battery goes on other end. Size of breaker, about 40 amp should be stamped on it. I found one at Camping World. I also replaced gen. battery with 2 golf cart batteries in series. Keep front coach battery to assist with battery boost as circuit breaker at gen. will trip if starting with boost. It is automatic reset. This way you have three batteries for coach operation. Iused replacement battery trays in gen. compartment to anchor batteries. Engine gen. charges all batteries on road. Converter charges coach batteries when plugged in and genset charges all coach batteries when running. Hope this helps.

If you need more let me know.

Bill Wallace

Date: Mon, 20 Apr 1998 09:24:14 -0700

From: "Heinz Wittenbecher"
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